Ozone and PAN Formation Inside and Outside of the Berlin ...easd.geosc.uh.edu/rappenglueck/pdf/2002_corsmeier_et_al_JAC.pdfDuring BERLIOZ in July/August 1998 in Berlin and Brandenburg,

Journal of Atmospheric Chemistry 42: 289–321, 2002.© 2002 Kluwer Academic Publishers. Printed in the Netherlands.

289

Ozone and PAN Formation Inside and Outside ofthe Berlin Plume – Process Analysis and NumericalProcess Simulation

U. CORSMEIER 1, N. KALTHOFF 1, B. VOGEL 1, M.-U. HAMMER 1,F. FIEDLER 1, CH. KOTTMEIER 1, A. VOLZ-THOMAS 2, S. KONRAD 2,K. GLASER 3, B. NEININGER 4, M. LEHNING 5, W. JAESCHKE 6,M. MEMMESHEIMER 7, B. RAPPENGLÜCK 8 and G. JAKOBI 8

1Institut für Meteorologie und Klimaforschung (IMK), Forschungszentrum Karlsruhe/UniversitätKarlsruhe, Postfach 3640, D-76021 Karlsruhe, Germany, e-mail: [email protected] für Chemie der Belasteten Atmosphäre (ICG2), Forschungszentrum Jülich, Germany3Institut für Verfahrenstechnik und Dampfkesselwesen (IVD), Universität Stuttgart, Germany4MetAir AG, Menzingen, Switzerland5Institut für Schnee- und Lawinenforschung, Davos Dorf, Switzerland6Zentrum für Umweltforschung (ZUF), Universität Frankfurt, Germany7Förderverein des Rheinischen Instituts für Umweltforschung, Universität zu Köln, Germany8Lehrstuhl für Bioklimatologie und Immissionsforschung, Technische Universität München,Germany

(Received: 23 October 2000; in final form: 22 March 2001)

Abstract. During the BERLIOZ field phase on 20 July 1998 a 40 km wide ozone-plume 30 to 70 kmnorth of Berlin in the lee of the city was detected. The ozone mixing ratio inside the plume was app.15 ppb higher than outside, mainly caused by high ozone precursor emissions in Berlin, resultingin a net chemical ozone production of 6.5 ppb h−1, which overcompensates ozone advection of–3.6 ppb h−1 and turbulent diffusion of –1.1 ppb h−1. That means, although more ozone leaves thecontrol volume far in the lee of Berlin than enters it at the leeside cityborder and although turbulentdiffusion causes a loss of ozone in the leeside control volume the chemical production inside thevolume leads to a net ozone increase. Using a semi-Lagrangian mass budget method to estimate thenet ozone production, 5.0 ppb h−1 are calculated for the plume. This means a fraction of about 20%of ozone in the plume is produced by local emissions, therefore called ‘home made’ by the Berlinemissions. For the same area KAMM/DRAIS simulations using an observation based initialisation,results in a net production rate between 4.0 and 6.5 ppb h−1, while the threefold nested EURADmodel gives 6.0 ppb h−1. The process analysis indicates in many cases good agreement (10% orbetter) between measurements and simulations not only in the ozone concentrations but also withrespect to the physical and chemical processes governing the total change. Remaining differencesare caused by different resolution in time and space of the models and measurements as well as byerrors in the emission calculation.

The upwind-downwind differences in PAN concentrations are partly similar to those of ozone,because in the BERLIOZ case they are governed mainly by photochemical production. While in thestable boundary layer at night and windward of Berlin 0.1 to 0.3 ppb are detected, in the centre ofthe plume at noon concentrations between 0.75 ppb and 1.0 ppb are measured. The O3/PAN ratiois about 80 to 120 and thus due to the relatively low PAN concentrations significantly higher than

290 U. CORSMEIER ET AL.

found in previous studies. The low PAN formation on 20 July, was mainly restricted by the moderatenonmethane hydrocarbon levels, whereas high PAN concentrations of 3.0 ppb on 21 July, are causedby local production in the boundary layer and by large scale advection aloft.

Key words: city plume, ozone formation, PAN formation, airborne measurements, process studies,numerical simulations, anthropogenic precursor.

1. Introduction

There is strong evidence for ozone in the troposphere over Europe to have doubledduring the twentieth century as a consequence of expanding industrialization and,in particular, growing mobility and transportation (Volz and Kley, 1988, Staehelinet al., 1994).

During high-pressure weather conditions, surface ozone concentrations in thepolluted continental boundary layer usually exhibit a pronounced diurnal cyclewith maxima during the day and minima at night. The daily maxima increasefrom day to day, while the nocturnal concentrations remain rather constant at afew ppb (Lutz, 1995; Neu, 1995; Obermeier et al., 1997). The maximum concen-trations depend on meteorological conditions and ozone precursor concentrations.Especially downwind of large urban agglomerations, significant changes in ozoneconcentrations due to increased precursor emissions are observed (Imhoff et al.,1995).

The basic photochemical origin of the enhanced ozone concentrations duringso-called summer smog episodes was noted in the 1950s (Haagen-Smit, 1952).Photooxidant formation in the outflow of urban areas was studied during, e.g.,ROSE (Cantrell et al., 1993), Southern Oxidant Study, SOS (Cowling et al.,1998), PEM-West (Hoell et al., 1996), North Atlantic Regional Experiment, NARE(Fehsenfeld et al., 1996; Penkett et al., 1998) and Schauinsland Ozone PrecursorExperiment, SLOPE (Kramp and Volz-Thomas, 1997; Volz-Thomas et al., 2000).Despite all these efforts a quantitative experimentally based understanding of theinteracting of the processes involved in tropospheric ozone formation is still lack-ing. In order to determine the local temporal change of the ozone concentration, it isnecessary to quantify the relative contribution of the different physical (advection,turbulent diffusion) and chemical processes.

Vogel (1991) first introduced a numerical mesoscale model to address theseprocesses properly for a city plume. According to the model, the increase ofthe ozone concentration in the morning hours in areas with high NO emissionsare exclusively caused by transport processes, and the locations of the maxi-mum chemical ozone production and maximum ozone concentration might differsubstantially. While the study of Vogel was limited to horizontal homogeneous con-ditions with respect to the meteorological variables, Vogel et al. (1992) extendedthis investigation to inhomogeneous terrain.

OZONE AND PAN FORMATION INSIDE AND OUTSIDE OF THE BERLIN PLUME 291

Turbulent mixing in the early morning and photochemical activity at noon arethe main reasons for the increase in ozone levels between sunrise and afternoon.At night, ozone concentrations decrease in the shallow, stable stratified surfacelayer because of dry deposition and chemical reactions, whereas ozone is approx-imately conserved in the residual layer aloft. In the morning, convection dissolvesthe nocturnal surface layer and transports ozone rich air from the residual layeraloft towards the surface. Thereafter, photochemical net production is responsiblefor the ongoing increase of ozone (Vogel, 1991).

Other photochemical oxidants that are formed beside ozone include peroxyacylnitrates, foremost peroxyacetyl nitrate (PAN) but also higher homologes like perox-ypropionyl nitrate (PPN). PAN formation is initiated by the reaction of OH radicalswith acetaldehyde. Initially formed acetylradicals are spontaneously converted intoperoxyacetyl radicals by atmospheric oxygen. They finally react with NO2 yieldingPAN. However this reaction competes with the reaction of the peroxyacetyl radi-cals with NO, forming NO2. An efficient PAN formation only occurs when NO2is in significant excess. Therefore the steady-state concentration of PAN must beproportional to the NO2/NO ratio. Since the steady-state concentration of O3 isalso proportional to this ratio, the steady-state PAN concentration should be pro-portional to the ozone concentration. The local budgets of PAN can be calculatedby using rate constants and concentration of precursors relevant for the formationpathway mentioned above (Jaeschke et al., 1996). Due to the findings of Schrimpfet al. (1998) who studied the behavior of PAN at a rural site in the environmentof Berlin, it can be assumed that PAN formation under the urban conditions ofthe Berlin city plume at fairly high temperatures during day time is governedby the steady-state concentration of the peroxyacetyl radicals. During daytimethe calculated PAN formation rates are mostly higher than observed changes inconcentration. This is due to the fact that significant amounts of PAN are lost bytransport phenomena. In that case PAN acts as an effective sink for local NOx andodd oxygen radicals (Kraus and Hofzumahaus, 1996).

Ozone abatement strategies require ozone forecasts with high accuracy. Ozoneprediction models which are up to now in operational use are not in all cases of suchquality. Reasons are the low vertical and horizontal resolution as well as simplifiedconvection schemes. The order of magnitude for each process (advection, turbu-lent diffusion, deposition and chemical net production) is between 0 and ±10 ppbozone per hour for typical central European weather situations and emission condi-tions in summer (Vogel, 1991). The magnitude of the individual processes changewith height above ground and stability of stratification. The processes are partleyindependent, so mutual compensation is possible.

In this paper airborne and ground-based meteorological and chemical data,measured during the first BERLIOZ special observation period (SOP) from 20and 21 July 1998 (Becker et al., 1999; Becker, 2000), are presented to analysethe composition, the structure and the development of the Berlin city plume. Local


Figure 1. Surface map of BERLIOZ measurement sites and of the flight pattern of the aircraftDO 128 (black), CESSNA 402 C (green) and DIMONA (orange) during the first SOP (20 to21 July 1998). The DIMONA and CESSNA flew perpendicular to the plume in two altitudesfor each traverse, while the DO 128 flew along the direction of the mean wind in three altitudesfrom southeast to northwest and back.

change, advection, turbulent diffusion and chemical net production of ozone arecalculated windward of Berlin, over the city and in the lee.

In the second part the experimental findings are compared with process studiescarried out with (i) the EURAD model (Memmesheimer et al., 1997) using a nest-ing technique and (ii) with the KAMM/DRAIS model system (Vogel et al., 1995).In the latter case observations of the measured flow in the domain and no nestingprocedures are used. Special aspects of air chemistry on the ozone formation andthe use of models as a tool to interpret measurements are discussed in a companionpaper of this issue by Becker et al. (2002).

2. Experimental Design

During BERLIOZ in July/August 1998 in Berlin and Brandenburg, Germany,chemical and meteorological parameters were measured at several sites, on teth-ered balloons and on board five aircraft, in order to quantity the processes involvedin the formation of an urban ozone plume. As shown in Figure 1, the sites werelocated along an axis extending from Lindenberg (LI) in the southeast to Lotharhof(LO) in the northwest of Berlin. The relevant experimental information about thesites including the vertical soundings is summarized in Table I. The instrumentationof the three aircraft equipped with meteorological and chemical instrumentationthat were active during the first SOP is summarized in Table II. A schematic viewof the flight pattern on 20 and 21 July is shown in Figure 1 as well.

The surface measurements, which were conducted throughout the campaign, in-cluded in-situ VOC determinations and high quality NOx measurements, as well asozone and PAN determination at Blossin (BL), Eichstädt (EI), Papstthum (PH) and


Table I. Surface sites of the BERLIOZ campaign with station number and abbreviation and datameasured at each site. ‘Met.’, indicates a set of meteorological data including temperature, humidity,pressure, wind speed and wind direction

No./ Location Surface measurements Vert. soundings

abbr. (long./lat.)

–3 Lindenberg O3, NO2, Met., radiation Met., O3LI (14.12/52.20)

–2 Neuendorf O3, CO, NOx , NOy , VOC, Met.

NE (13.90/52.10)

–1 Blossin O3, PAN, CO, NOx , NOy , VOC, O3BL (13.80/52.26) Met.

0 Wildau O3, NO, NO2, CO, SO2,

WI (13.66/52.33) Met.

0 Tempelhof O3, NO, NO2, CO, SO2, Wind speed, wind direction,

TH (13.40/52.48) dust temperature

0 Berlin O3, PAN, CO, NOx , NOy , VOC, O3, Met.

CH (13.37/52.52) Met.

0 Frohnauer Turm 4 m agl: O3, NO, NO2, NOx , CO, SO2, VOC, dust, temp., humidity

FT (13.30/52.66) 324 m agl: O3, NO, NO2, NOx , PAN, VOC, Met.

+1 Eichstädt O3, PAN, CO, NOx , NOy , VOC, Met., O3, NO2EI (13.12/52.69) Met.

+2 Papstthum O3, PAN, CO, NOx , NOy , VOC, Met., O3, NO2, NOx , VOC

PH (12.93/52.85) Met.

+3A Dessow Met., energy balance, O3, NO, Met., O3DE (12.50/52.90) NO2, CO

+3 Braunsberg/Lotharhof NO, NOx , NOy , O3, CO, HCHO, Wind speed, wind direction,

BR/LO (12.85/53.05)/(12.80/53.10) H2O2, VOC, Met. O3

+3B Menz O3, PAN, CO, NOx , NOy , VOC, Met., O3ME (13.02/53.10) Met., energy balance

Menz (ME). In addition, a corresponding suit of instruments was set up on top ofthe Frohnau Tower (FT) at an altitude of 324 m agl. Though strictly speaking, thissite is not a surface site, it allows continuous observations in the urban boundarylayer. For NOx , sensitive chemiluminescence instruments with photolytic convert-ers (ECO-Physics CLD 700Al-ppt with PLC 760) were deployed at EI, PH andME. PAN was measured at BL, PH and ME using identical gas-chromatographicsystems (GC) with capillary column and ECD detector (Meteorologie Consult,Glashütten). At EI and FT identical Scintrex LPA-4 PAN analysers were installed.


Table II. Equipment for meteorological and chemical measurements onboard the aircraftDO 128, CESSNA 402 C and DIMONA

Parameter Sensors

DO 128 CESSNA 402 C DIMONA

Temperature Rosemount PT 100 Vaisala-Thermistor Thermoelement

Humidity Aerodata-Humicap; Vaisala

Lyman-alpha capacitive Sensor

Dewpoint Dewpoint mirror TM3 Dewpoint mirror

Pressure Rosemount Pitot-probe Rosemount

5-hole-probe 5-hole-probe

Height Radar altimeter; GPS Pressure; GPS Radar altimeter

Position Lasernav; GPS GPS GPS (TANS Vector)

Wind (horizontal) 5-hole-probe; GPS Pitot-probe, GPS 5-hole-probe; GPS

Wind (vertical) 5-hole-probe 5-hole-probe; GPS

Surface temperature Heimann KT 4

O3 Environment O3 41M TE 49 Ozone sensor

(UV-absorption) (UV-absorption) (UV-absorption)

Ozone flux sensor

(Chemilum.)

NO NOxTOy TE 42 S NOxTOy(Luminol-Chemilum.) (Chemilum.) (Luminol-Chemilum.)

NO2 NOxTOy NOxTOy(Luminol-Chemilum.) (Luminol-Chemilum.)

NOx TE 42 S

(Chemilum.)

NOy NOxTOy(Luminol-Chemilum.)

Ox GPT/Chemilum.

VOC Canistersampling Canistersampling Airmo VOC HC1010

PAN Kryosampling NOxTOy

CO2 IR-absorption IR-absorption


Vertical profiles of ozone and meteorological data (pressure, temperature, hu-midity and wind) were measured at LI, EI, PH, ME and Dessow (DE), usingradiosondes and tethered balloons, while vertical profiles of NO2 and NOx wereobtained at PH by tethered balloons.

The instrumentation of the three aircraft DIMONA (operated by MetAir),CESSNA 402 C (operated by ZUF) and DO 128 (operated by the Institute on FlightGuidance and Control of the University of Braunschweig and by IMK), whichdeliver data for this study, is shown in Table II. The DIMONA was equipped withinstruments for in-situ measurements of NO2, NOx , NOy , PAN, O3, HCHO, H2O2,and hydrocarbons (in the range C4–C10). The hydrocarbon measurements aboardthe aircraft were made quasi-continuously with an Airmotec HC1010 automaticgas chromatograph with sampling time of 10 minutes. For the NOy componentsand Ox = O3 + NO2, a recently developed multichannel instrument on the basisof the chemiluminescence of NO2 with luminol in combination with different con-verters was deployed for the first time. Meteorological parameters were recordedwith high time resolution. The flight pattern (Figure 1) were predetermined in aquasi-Lagrangian approach so that the city plume of Berlin was traced two timesat approximately the distance determined from wind speed and direction.

The CESSNA 402 C aircraft was equipped with a gas chromatograph for air-borne PAN measurements. Samples were taken every ten minutes. The instrumentwas identical with the gas chromatographic systems used at the ground stations. Ithad passed the same procedures for quality assurance. Ozone concentrations weremeasured using a commercial UV-absorption instrument. The time resolution was10 seconds.

Onboard the DO 128, high frequent measurements of meteorological parame-ters and trace constituents were performed (Table II). Together with INS- andGPS-navigation a sample frequency of 25 Hz is realised. Using a mean groundspeed of 65 m s−1, the resolution of the measurements is less than 3 m. Forthe BERLIOZ project the aircraft’s research capabilities were enlarged by theintegration of a sensor package for the measurement of NO, NO2, CO2 and O3with frequencies between 1 Hz and 20 Hz, and detection limits of 1 ppb. NOand NO2 measurements were done by the same instrument as used onboard theDIMONA, CO2 measurements by a LICOR instrument and O3 data were detectedby a fast ozone sensor (Güsten et al., 1992) stabilized by an O3 41 M monitor. Thisequipment does not only allow the detection of mean quantities, but also, usingthe eddy-correlation technique, to calculate small-scale turbulent fluxes of watervapour and ozone as well as the turbulent flux of sensible heat. Details concerninginstrumentation, data and the measuring concept of BERLIOZ can be found inBecker et al. (1999) and Becker (2000).

The function of meteorological and chemical sensors onboard all aircraft and ofthe chemical equipment at the ground stations as well as the observance of strictdata quality goals was guaranteed by the quality control procedures done beforeBERLIOZ by an independent quality control team (Kanter et al., 2002, this issue).


The gas analysers on the ground and onboard the aircraft were controlled by mea-suring a calibration gas of unknown concentration and by a long-term measurement(24 hours) of ambient air at the same site. The airborne equipment was additionallycontrolled by an intercomparison flight wing by wing of the aircraft. For details seeKanter et al. (2002, this issue).

3. Results

3.1. THE BERLIN-PLUME OF 20/21 JULY 1998

3.1.1. Large-Scale Forcing and Boundary Layer Development

The meteorological conditions during the SOP from 20 and 21 July were domi-nated by a high-pressure system over Poland and a low-pressure system over GreatBritain. This results in a large-scale flow near the ground in the Berlin area from170◦ between 06 and 18 UTC with a maximum wind speed of 4 ms−1 duringdaytime. The minimum temperature at 04 UTC in the morning was 10 ◦C, themaximum was 30 ◦C at 16:30 UTC. In the afternoon a weak warm front withoutsignificant weather activity passed the area and caused the wind to turn right withheight. So the wind blew only in the surface layer and in the lowest flight level(370 m) from southeasterly directions (Figure 2). In the levels aloft (680 m and990 m) winds from south to southwest prevailed and caused the city plume todevelop and to move more in the north of the city, than in the northwest. The warmfront additionally transported air with high ozone mixing ratios from the south-west of Germany to the investigation area, as can be seen by trajectory analysis(Andersson and Steinhagen, 2000). This is obvious on top of the Frohnau Tower,where a significant increase in the ozone mixing ratios from 73 to 96 ppb could beobserved at 19 UTC (Figure 3). This increase was also accompanied by elevatedPAN values reaching about 1 ppb. At this time of the day the layers aloft werealready decoupled from the surface layer due to a strong thermal inversion. Similarobservations could be made in the night from 6 to 7 August, when PAN valueseven reached 2.5 ppb representing the maximum values throughout the BERLIOZcampaign (Rappenglück et al., 2001). This latter event was also associated withadvection processes along a warm front. Both events were marked by vertical windshears and enhanced wind speeds up to 11 m s−1 (20 July) and 16 m s−1 (6 and 7August), respectively, in the boundary layer.

Under these synoptic conditions a mixed layer developed which reached up to1000 m above ground level (agl) at noon and even increased up to 1900 m agl at16 UTC at Dessow (DE). Within the mixed layer a moderate wind speed between5 m s−1 and 7 m s−1 was found. The wind direction turned from southeasterlywinds at the surface to southwesterly winds at the top of the mixed layer. Above thePBL westerly winds dominated. During the day the mixed-layer potential tempera-ture increased from 293 K in the morning to 303 K in the evening. The same orderof temperature increase could be found at the elevated levels at stations windward


Figure 2. Surface wind field in the Berlin area at 20 July 1998 at 07 and 15 UTC. Arrows inwhite squares indicate measurements between 4 m and 10 m height. The white arrow showsthe wind at the Frohnau Tower (FT) at 324 m agl. The remaining arrows are KAMM modelresults at 16 m above ground.


Figure 3. Time series of O3, PAN and NOx at Eichstädt (EI) and at 324 m height at theFrohnau Tower (FT) on 20 and 21 July 1998.

of Berlin at Lindenberg (LI), in the city at Tempelhof (TH) and in the lee side ofthe city at Papstthum (PH) and Dessow. As shown by Steidl (1999) the temperatureincrease results from horizontal advection of warm air (0.3 to 0.4 K h−1) and thedivergence of the sensible heat flux (0.5 K h−1).

On 21 July, the low-pressure system propagated eastward and caused precipita-tion and thunderstorms in the investigation area during the second half of the day.The temperature increased from 20 ◦C in the early morning up to more than 35 ◦Cat 13:30 UTC and the wind turned to southwest and west throughout the wholeboundary layer, while southerly winds blew above. Because of the instationary


synoptic scale flow no investigations of the city plume development could be madein the afternoon of 21 July.

3.1.2. Surface Measurements and Vertical Profiles

Figure 4 shows the concentrations of PAN, NOx and O3 at the surface sites BL, EI,PH, and ME on 20 and 21 July. The advection of polluted air was observed on bothdays of the SOP at all leeward sites. The concentrations of NOx and anthropogenicVOC (not shown), increased at EI, PH and ME (in consecutive order and decreasingconcentration). At PH, NOx concentrations reached peak values around 18 ppb on20 July and 27 ppb on 21 July. The concentrations at the upwind site BL remainlow, between 2 and 10 ppb.

The diurnal pattern of O3, on the other hand, is quite similar at all three sites.The concentrations increase around 06 UTC from relatively low values of 5 to10 ppb and reach maximum values of 65 to 70 ppb on 20 July and 87 ppb (EI)to 94 ppb (FT) on 21 July, respectively (Figure 3). However, it should be notedthat maximum ozone values of 96 ppb occurred on 20 July, 20:30 UTC on topof the Frohnau Tower. This behaviour highlights the fact, that the photochemicalozone net production inside the city plume of Berlin is not easily distinguishedfrom downward mixing and/or advection from outside the area. The photochemicalproduction is clearly seen, however, in the PAN data. In the morning of 20 July,before the break up of the nocturnal inversion, PAN mixing ratios are similar at allfour sites, with a minimum of 50–150 ppt around 04 UTC. At sunrise (05 UTC),PAN at BL increases weakly and remains around 300 ppt throughout most of theday, whereas the PAN mixing ratios at the leeward sites increase more or less si-multaneously to reach maximum values of 1 ppb around 12 UTC. Thereafter, PH isno longer located in the plume of Berlin, which explains the decreasing PAN valuesas compared to ME. The observed diurnal variations of the PAN concentrations arecomparable to those found by Schrimpf et al. (1998), during summer 1994 at a ruralsite in Mecklenburg, north of Berlin. However the absolute concentration values ofthese authors were lower, because the city plume of Berlin never influenced theirsite.

Figure 3 displays the time series of ozone, PAN and NOx as observed concur-rently at the surface site EI and on top of the FT in the urban boundary layer. Theozone time series at FT can be regarded as an enveloping curve: usually no ozonemeasurements obtained on any surface site exceeded those values obtained at FT.In the early morning of 20 July, some sharp variations of both ozone and NOxoccur at FT. This was probably due to the emissions from a factory stack near thetower, as proofed by the measurements of the DO 128 (not shown). During theseevents, PAN, too, shows increased values up to 850 ppt at the FT. As the windturns to southeasterly directions at EI at about 04 UTC on 20 July, the urban plumestretches to EI leading to increasing NOx values. At 07 UTC the thermal inversionvanishes. Enhanced vertical mixing rapidly leads to a homogeneous distribution ofthe trace gases within the boundary layer. NOx values decrease at EI, while NOx


Figure 4. Diurnal cycle of PAN, NOx and O3 upstream of Berlin at 20 July (left) and at 21 July(right) 1998 at Blossin (BL, ×) and downstream at Eichstädt (EI, ◦, 20 km), Papstthum (PH,�, 40 km) and Menz (ME, +, 60 km). The numbers give the distance of the lee sites to thecentre of Berlin.

rich surface air masses reach the FT causing a corresponding decline in ozonemixing ratios. PAN at FT only slightly increases. However, with its values rangingfrom 500–600 ppt PAN exhibits higher values than the surface sites at this timeof the day as shown in Figure 4. In the subsequent hours PAN mixing ratios at FTfollow the increasing PAN time series at the surface sites. Accordingly, a PAN peakof about 900 ppt occurs at noon. Though afterwards, PAN values at FT decrease


the way most of the other surface sites do, PAN at FT remains at higher levels thanat EI, for instance. FT’s location on the border of the urbanized area of Berlin maybe the reason for this behaviour as FT may receive polluted urban air.

Well-mixed boundary layer conditions persist on 20 July, until 17:00 UTC whenatmospheric stratification became more stable due to the incoming warm front. Onthe following day it is not before 8:00 UTC that the thermal inversion vanishes.Contrary to the preceding day the urban plume thus remains trapped in the shallownocturnal boundary layer for an hour longer and is not affected by vertical dilutionprocesses. The urban NOx plume has already passed EI when finally at 08 UTCthe inversion layer breaks up. Again, this process rapidly leads to an enhancementof NOx mixing ratios at FT. Ox at both sites immediately approaches the samevalues, a feature that has also been observed on the preceding day. PAN values atFT abruptly rise from low 40 ppt up to 600 ppt. At about 10 UTC the wind direc-tion commences to turn from southeast to southwest and reaches west at 14 UTC.Though this time period is marked by both a well-pronounced broad ozone peakwith maximum values of 94 ppb at FT and a sharp PAN peak of more than 1 ppbat FT. The urban plume is not as well defined as it was the case on 20 July, due toinstationary wind directions.

On both days O3/PAN ratios at FT as observed at noontime lie in the rangebetween 80–90. For the entire campaign average daytime O3/PAN ratios (09 to18 UTC) were about 102 (Minimum: 46) at FT and about 117 (Minimum: 35)at EI, for instance. These values are higher than found in previous studies inGermany (Kourtidis et al., 1993), who found O3/PAN ratios mainly ranging from17–26 (urban area of Munich) to 37–51 (rural area in the Bavarian Forest). PANformation may be either restricted by thermal decomposition, low NO2/NO ratiosor the lack of precursors, in particular nonmethane hydrocarbons. Atmosphericlifetime of PAN depends on thermal decomposition and the NO2/NO ratio. It maybe calculated according to Ridley et al. (1990). For the entire BERLIOZ campaignthe average PAN lifetime was about 14.5 h. However, mainly due to the highambient air temperatures on 20–21 July, PAN lifetime showed mimimum valuesranging from 40–180 min from 20 July, 13 UTC until 21 July, 18 UTC. This isonly slightly higher than other urban studies revealed (e.g., Rappenglück et al.,2000). However, in these studies O3/PAN ratios were almost by a factor 10 lowerthan during BERLIOZ. We suggest that the primary reason for this feature aredifferent atmospheric loads of nonmethane hydrocarbons since O3/PAN ratios arelikely to decrease with increasing nonmethane hydrocarbon values (Kourtidis etal., 1993). As a consequence, PAN formation in the Berlin area may have beenrestricted by the overall moderate nonmethane hydrocarbon levels encounteredduring BERLIOZ (Winkler et al., 2002, this issue).

Figure 5 shows a two dimensional interpolation of the vertical profiles of NOxwhich were measured on the tethered balloon at PH (Glaser et al., 2000). Theprofiles clearly confirm the arrival of a plume on 20 July, at 08–09 UTC, with thehigh NOx concentrations of about 15 ppb extending up to 700 m. The relatively


Figure 5. Isoplete diagrams of NOx measured at Papstthum (PH) by means of a tetheredballoon on 20 and 21 July 1998. The dotted lines mark the position of the balloon.

high concentrations measured in the early morning are likely due to weak localemissions into the stable stratified nocturnal boundary layer of about 100 m thick-ness at stagnant winds (


Figure 6. Aircraft measurements of O3, NOx and PAN made by CESSNA 402 C and DI-MONA in two cross sections (top: near the city; middle: 60 km leeside of the city) in differentheights and NOx and O3 measurements made by DO 128 (�) in 3 heights and DIMONA (◦)in 1 height on a along wind pattern from the windward side over the city to the lee between10 UTC and 15 UTC at 20 July 1998.


Figure 7. The same as Figure 6 but in the morning between 07 and 12 UTC at 21 July 1998.

layer is about 1400 m high. The corresponding NOx values are 6 to 12 ppb in theplume and 3 to 6 ppb outside. PAN is high (762 ppt) downwind of Berlin in theair above ME, in the centre of the plume and lower (423 to 521 ppt) at its edge.The PAN-concentrations indicated in Figure 6 are aircraft measurements along asampling distance of ∼3.3 km.

At the traverse near the northern city border of Berlin the situation is justthe other way round (Figure 6, middle diagrams): in the boundary layer beneath


Figure 8. Vertical profiles of ozone mixing ratios measured by tethersondes in the morningand in the late afternoon at Dessow (DE) outside and at Menz (ME) inside the Berlin plume.

1200 m there is at 11 UTC a significant NOx plume of ≈30 km width with mixingratios between 9 and 18 ppb. Outside the plume 3 to 6 ppb NOx are measured.Ozone and PAN are well mixed in the boundary layer. The concentrations are about65 ppb for O3 and 500 ppt for PAN. Similar values we find at FT (Figure 3). Thedata measured on the along wind pattern from windward Berlin to the lee proof thehitherto findings (Figure 6, lower diagrams). Ozone is low (65 ppb) windward andover the city and increases in the afternoon within the boundary layer up to 75 to80 ppb, the more the aircraft flies to the north of Berlin. The NOx data are just theopposite: high (15 to 18 ppb) over the city and low (9 to 12 ppb) at the leeside inthe centre of the ozone plume.

Summarising, the development of an ozone plume in the boundary layer of≈40 km width beginning 30 km in the lee of Berlin is detected. The ozone concen-trations are 10 to 15 ppb higher than outside the plume. The PAN concentrationsare 200 to 300 ppt higher and NOx is less than in the lee near the city. Caused by


the turning of the wind, the plume propagates to north-west in the morning and tonorth after 11 UTC.

At 21 July, the situation is quite different because of lower mixing layer heightand large scale advection of ozone and PAN. In the morning between 8 and 9 UTCthe mixed layer is less than 400 m high as measured at DE. Very high NOx mixingratios up to 44 ppb are measured crossing a 30 km wide plume direct north of thecity in 200 m height. East and west of the plume 9 to 19 ppb are detected and inthe stable stratified residual layer in 800 m the mixing ratio is 4 to 9 ppb (Figure 7,middle diagrams). As a consequence ozone (50 to 70 ppb) and PAN (0.5 to 1.0 ppb)are low in the 200 m traverse and higher, 80 to 100 ppb for ozone, 1.5 to 2.0 ppb forPAN, in the upper stable traverse, where horizontal advection plays an importantrole (Andersson and Steinhagen, 2000).

The far lee traverses are flown between 10 and 11 UTC, 70 km north of Berlin.At this time the mixing layer height is about 900 m. The NOx mixing ratio isbetween 9 and 19 ppb within the mixing layer and aloft. In the plume it decreasedfrom 44 ppb near Berlin to 14 ppb far in the lee. Simultaneously ozone increasedfrom 55 to 95 ppb in the mixed layer at 300 m height (Figure 7, upper diagrams).But there is no difference in the ozone mixing ratios in the mixed layer and in theair above up to 2000 m. Here the large scale transport seems to be responsible forthe high concentrations of up to 100 ppb. Similar is the interpretation of the PANmeasurements. PAN is formed in the plume leading to mixing ratios up to 3.0 ppbbelow 800 m. In the air aloft horizontal PAN transport results in mixing ratios of2.5 ppb. The relative high concentrations in the range of 1 to 3 ppb are remarkable.Since PAN has no other source than its production by photochemical reactions theoccurrence of such high concentrations is a clear indication for the local formationof photochemical smog in the city plume of Berlin. The variations of the PANconcentrations along the flight tracks are closely linked to the variations of thesimultaneously measured O3 concentrations. This confirms that at noon also O3 ismainly formed by photochemical reactions of those precursors that are emitted bylocal sources.

The measurement on the along wind pattern (Figure 7, lower diagrams) under-line this interpretation. At 10 UTC the DIMONA (◦) detected low ozone (70 ppb)and PAN (0.5 ppb) and high NOx values (44 ppb) over the city. Turning north,ozone (90 ppb) and PAN (1.5 ppb) increased and NOx decreased (4 ppb). Duringthe formation of the ozone city plume the DO 128 (�) measurements later in time(11 to 12 UTC) show higher ozone concentrations up to 90 ppb in all three levelscaused by advection (upper and middle level) and vertical mixing (lower level).The decrease of ozone far in the lee is caused by the flight pattern directed to northand so leaving the city plume, propagating to north-east.


3.2. PROCESS ANALYSIS BASED ON MEASUREMENTS

3.2.1. Advection, Diffusion and Production of Ozone

Equation (1) describes the local change of the ozone mixing ratio (a) caused byadvection (b), molecular diffusion (c), turbulent diffusion (d), chemical production(e) and loss (f). In the following the terms (e + f ) are summarized as chemical netproduction rate

∂C

∂t= −uj ∂C

∂xj+ vc ∂

2C

∂x2j− ∂(u

′jC

′)∂xj

+ P − L ,

(a) (b) (c) (d) (e) (f)

(1)

where C is the ozone concentration, uj , (j = u, v,w) are the components of thewind vector, xj , (j = x, y, z) are cartesian coordinates, vc is the molecular dif-fusivity coefficient, t is time and the overbars denote mean quantities. Neglectingmolecular diffusion (c), the divergence of the horizontal turbulent fluxes of term(d) and turning the system in the direction of the mean wind u, the budget equationfor the local change of the mean ozone concentration is

∂O3

∂t= −u∂O3

∂x+ w∂O3

∂z− ∂(w

′O ′3)∂z

+ P O3 − LO3 ,(a) (b) (c) (d) (e) (f)

(2)

The terms (a) to (d) have been calculated from the DO 128 aircraft data and w istaken from the output of the forecast model of the German Weather Service. Thechemical production and loss (e, f) was calculated as residuum (Steidl, 1999).

Estimating the local change of ozone, the turbulent diffusion is an importantprocess, which is not easy to quantify by measurements. Up to now only a few fluxmeasurements (e.g., Lenschow et al., 1980) and budget studies (Ritter et al., 1990)are known from the literature. During BERLIOZ an analyser for measurements ofhigh frequent ozone fluctuations up to 10 Hz was operated onboard the DO 128.Vertical ozone flux profiles have been calculated between the surface layer (60 m)and the upper part of the boundary layer (1300 m) for the afternoon of 20 July 1998(Table III).

Compared to the case in the early morning (not discussed here), the turbulentozone flux gives a considerable contribution to the local change of ozone. Down-ward ozone fluxes of about –0.3 ppb m s−1 are detected in all three levels windwardof the city. The flux divergence is low in this case and there are hardly any changesin the ozone mixing ratio caused by turbulent diffusion. The amount of the flux isequivalent to values of –0.42 ppb m s−1 found by Godowitch (1990) and –0.21 ppbm s−1 measured by Affre et al. (1999) over agriculturally used areas. Over the citythe divergence of the ozone flux, which increases with approach to the ground, issignificant. This divergence is caused by the ozone minimum in the near surface


Table III. Mean ozone mixing ratios at 20 July 1998 between 14 UTC and 15 UTCwithin the planetary boundary layer and vertical profiles of the turbulent ozone fluxcalculated from DO 128 measurements of the turbulent ozone- and vertical windfluctuations

Height Windward City Lee

in m Ozone Ozone flux Ozone Ozone flux Ozone Ozone flux

in ppb in ppb m s−1 in ppb in ppb m s−1 in ppb in ppb m s−1

1300 73.3 66.0 62.2

990 65.7 –0.32 61.9 –0.13 65.7 +0.08

680 61.4 –0.27 61.7 –0.31 68.6 +0.06

370 61.0 –0.33 61.8 –0.60 67.0 –0.11

60 68.7 47.4 66.3

layer over the city, produced itself by chemical loss of ozone due to anthropogenicemissions of NO and because of enlarged ozone deposition due to high turbulencein the surface layer. This results in a significant reduction of the ozone mixing ratioin the lower layer over the city in comparison to the windward case. On the lee sideof the city over large forests the turbulent ozone flux reaches its lowest values in thisstudy. The flux varies from 0.08 ppb m s−1 at 990 m to –0.11 ppb m s−1 at 370 m.Krautstrunk et al. (2000) have measured fluxes between –0.08 and –0.18 ppb m s−1downwind of urban and industrial agglomerations. The flux divergence now playsa minor role in changing the vertical profile of the ozone mixing ratio.

Table IV summarizes the measured and modelled results of the process analysisof the Berlin plume in three heights windward at Blossin, over the city at Frohnauand in the lee at Menz and Papstthum. Upwind of Berlin between 14 and 15 UTCan average ozone increase of 5.4 ppb h−1 is detected, mainly caused by advectionof ozone rich air in the lower and upper layer. Backward trajectories show, that theozone in the upper boundary layer has its origin in high ozone net production insouth and southwest Germany (Andersson and Steinhagen, 2000). Vertical advec-tion, turbulent diffusion and ozone net production are very low upwind the city.Over the city the local change of ozone mixing ratio is near zero, because negativeadvection of –1.6 ppb h−1 and downward turbulent diffusion of –2.7 ppb h−1 arecompensated by a mean ozone net production rate of 3.5 ppb h−1. About 50 kmleeward of Berlin, between Papstthum and Menz, the local increase of the ozonemixing ratio is 1.8 ppb h−1. This results from negative advection of –3.6 ppb h−1and negative turbulent diffusion of –1.1 ppb h−1 and a net production rate of 6.5 ppbh−1 that overcompensates advection and turbulent diffusion. This net productionrate agrees well with calculations of Mihelcic (2000), who found for Papstthuman ozone production of 7.5 ppb h−1 for the same time. EURAD simulations byMemmesheimer result in net production rates of 4.0 to 6.0 ppb h−1 within the


Tabl

eIV

.C

ontr

ibut

ions

ofad

vect

ion,

turb

ulen

tdi

ffus

ion

and

chem

ical

net

prod

ucti

onto

the

loca

lch

ange

ofoz

one

inth

epl

anet

ary

boun

dary

laye

ral

ong

the

DO

128

flig

htpa

tter

non

20Ju

ly19

98at

14:3

0U

TC

inpp

bh−

1.T

heca

lcul

ated

chem

ical

neto

zone

prod

ucti

on〈�

chem

O3〉a

ndth

eco

rres

pond

ing

KA

MM

/DR

AIS

sim

ulat

ions

are

show

n

Loc

atio

nH

eigh

tL

ocal

chan

geH

oriz

onta

lV

erti

cal

Tur

bule

ntN

etpr

oduc

tion

Net

prod

ucti

on

adve

ctio

nad

vect

ion

diff

usio

n(c

alcu

late

d)(K

AM

M-s

imul

atio

n)

Win

dwar

d37

0m

Blo

ssin

5.1

±0.

34.

4±

1.0

0.0

−0.1

±0.

30.

7±

1.6

4.3

±3.

3

680

mB

loss

in4.

7±

0.4

1.3

±0.

30.

0−0

.1±

0.3

3.4

±1.

03.

8±

0.2

990

mB

loss

in6.

3±

0.3

7.5

±1.

10.

1±

0.1

−0.1

±0.

3−1

.2±

1.8

2.7

±0.

2

Cit

y37

0m

Fro

hnau

−0.1

±0.

1−1

.9±

0.4

0.0

−2.7

±0.

74.

5±

1.1

3.9

±1.

9

680

m−2

.0±

0.2

0.0

−2.7

±0.

74.

6±

1.0

4.2

±0.

5

990

m1.

0±

0.2

0.0

−2.7

±0.

71.

6±

1.0

3.7

±0.

3

Men

zPa

pstt

hum

Lee

370

m2.

1±

0.1

1.9

±0.

2−3

.9±

0.7

0.0

−1.1

±0.

26.

9±

1.0

4.7

±0.

8

680

m1.

3±

0.1

2.1

±0.

3−3

.2±

0.7

0.0

−1.1

±0.

26.

0±

1.1

4.1

±0.

4

990

m−3

.8±

0.6

0.0

−1.1

±0.

26.

6±

1.1

3.5

±0.

1


ozone plume in the level between 310 and 430 m for the same time. Over the citythe simulated ozone net production is between 0.0 and 4.0 ppb h−1, while windwardof Berlin an ozone net production of up to 2.0 ppb h−1 is calculated by the model(Figure 9). Vogel and Hammer, using the KAMM/DRAIS model get 4.7 ppb h−1 inthe lee 3.9 ppb h−1 over the city and 4.3 ppb h−1 at the windward side (Figure 11).Details see section 3.3.

3.2.2. Mass Budgets

Table V summarizes the results of budget calculations that are derived from theexperimental data following an approach described by Lehning (1998), Lehning etal. (1998a, 2000). The method is based on calculating both, the advective and (ifavailable) the turbulent fluxes of trace gases at different altitudes within a controlvolume around the measurements. The calculation uses the complete data set ofmeteorological parameters and trace gas concentrations, which may be irregularlydistributed in time and space. Slightly different from the original method, the fluxesare calculated in a semi-Lagrangian way, as will be discussed in detail in Lehning etal. (2000). Briefly, a window that moves with the mean wind at each altitude level(dz = 50 m) is introduced for the weighting of the data. This has the advantagethat the often unrealistic assumption of stationarity can be relaxed at first approx-imation. However, a high data density like in the BERLIOZ data set is requiredfor the semi-Lagragian calculation. For each grid cell, a wind vector and a tracegas or aerosol concentration are thus determined. The horizontal flux is then theproduct of the wind component perpendicular to the grid cell and the concentrationvalue. All the horizontal fluxes through the grid cells on the box boundaries aresummed. A mean vertical subsidence velocity is included, either empirically fromsequentional vertical profiles, or to balance the mass budget. This budget yields theaccumulation of the substances in the boundary layer.

By including exchange with the free troposphere (Lehning et al., 1998b) anddry deposition to the surface in the budget, an estimation of the total boundarylayer budget results which can be interpreted in terms of a fraction of ‘homemade’pollution and a net production rate. Exchange with the free troposphere is cal-culated using the parameterisation by Lehning et al. (1998b), which is using theeddy-correlation method when data are available, but uses the gradients when tur-bulence data are missing. The deposition fluxes are calculated using representativedeposition velocities for the trace gases and a diffusivity approach is used for heatand moisture exchange.

The three intensive days in BERLIOZ with detectable local ozone formationshow ozone accumulation rates in the boundary layer between 0.5 and 3.7 ppbh−1. The results include sensitivity studies, (i) by selection of subsets of data, e.g.,discarding the ground stations or selecting the ‘best suited’ aircraft tracks and (ii)by variation of the interpolation parameters. The ranges given in Table V includeall sensitivity cases, except for a few isolated and unrealistic outliers. The corre-sponding net ozone production rates vary between 4.5 and 5.4 ppb h−1 for 20 July,


Figure 9. EURAD simulations of NOx (top) and O3 (middle) in the Berlin area for 20 July1998 in the morning (left) and at noon (right) in the layer between 0 and 40 m and of thechemical net production rate of ozone for the same area between 310 m and 430 m aboveground (bottom right) and at the surface (bottom left), both at 14 UTC.


Table V. Mass budgets of trace gases during three BERLIOZ special observation periods

Substance Monday, 20 July Tuesday, 21 July Saturday, 8 August Average

Accumulation rate (ppb h−1)O3 2.8–3.7 1.5–2.1 0.5–2.7 2.2

NOx 0.79–0.88 0.32–0.47 0.19–0.51 0.53

2-Methylbutane 0.0011–0.0019 0.0083–0.0090 0.0083–0.0113 0.0067

Benzene 0.0026–0.0044 0.017–0.020 0.014–0.015 0.0120

Ethylbenzene 0.0022–0.0024 0.0038–0.0042 0.0026–0.0027 0.0030

Toluene 0.033–0.036 0.041–0.044 0.036–0.040 0.0383

Accumulation ratios (mole/mole)

O3/NOx 3.5–4.2 4.5–4.7 2.7–5.3 4.2

Toluene/benzene Unreliable 2.2–2.2 2.6–2.7 2.4

Net production (ppb h−1)O3 4.5–5.4 1.8–2.9 1.5–3.7 3.3

NOx 1.0–1.2 0.42–0.58 0.21–0.53 0.66

Ox (O3 + NO2) 5.5–6.6 2.2–3.5 1.7–4.2 4.0

Home made fraction (%) a

O3 18–21 9–14 5–10 13

NOx 52–57 22–35 13–30 35

2-Methylbutane 2 3 4 3

Benzene 20 36 84 47

Ethylbenzene 28 16 62 35

Average of aromatic HCs 50 28 99 59

a For NOx and O3 from detailed budget, coarse estimate for HCs.

with fractions of homemade ozone pollution between 18 and 21%. The net ozoneproduction on 20 July is ≈1.5 ppb h−1 lower than what is derived from the turbulentfluxes of the DO 128 and 0.9 ppb h−1 higher than KAMM/DRAIS model results(Table IV). For the ozone precursors NOx and selected aromatic hydrocarbons,local emissions seem to be responsible for about half of the pollution observed inthe leeward side of the box (‘homemade fraction’ in Table V).

3.3. NUMERICAL PROCESS SIMULATION

The measurements during the BERLIOZ-SOPs, characterizing the developmentof a city plume in time and space, are a valuable dataset for numerical processsimulation and model evaluation. Two groups operating different comprehensivemodel systems used the BERLIOZ data to examine the forecast capabilities of


their models, to study downscaling techniques like nesting and to compare themeasured and simulated local changes in ozone concentration inside and outsidethe city plume. Even comprehensive model systems have several sources of errors,which are difficult to quantify in detail, partly due to non linear error propagation.To give two examples emission data usually differs from real world emissions andnumerous processes incorporated in comprehensive models are based on parame-terisations. Both model systems used in this study were extensively compared withobservations in the past (e.g., Memmesheimer et al., 1997; Nester, 1995; Vogelet al., 1995). Such comparisons were mostly based on measured and simulatedconcentrations. Now the BERLIOZ campaign gives the opportunity to compareindividual observed and simulated processes, in our case the net chemical produc-tion of ozone, whereas internal aspects of air chemistry on the ozone productionare published by Becker et al. (2002) in this issue. Both model systems usedthe same data set for the anthropogenic emissions as input data for the area ofBerlin/Brandenburg. These emissions were determined by Wickert et al. (2001).

3.3.1. The EURAD Model

The European Air Pollution Dispersion Model EURAD (Hass et al., 1995;Memmesheimer et al., 1997) has been used to simulate the chemical and dynam-ical processes which control the concentration of atmospheric trace gases in theBerlin/Brandenburg area. The contributions of advection, turbulent diffusion, depo-sition and chemical net production of ozone are calculated to analyse the temporalchange of ozone concentrations.

The nesting option of the EURAD modelling system has been used to performthe calculations from the European scale down to the urban scale of Berlin and thenearby regions. One way nesting allows to include the effect of processes in themother domain on the embedded nests but not vice versa. For the application tothe Berlin/Brandenburg area a mother domain (54 km grid resolution) with threeembedded nests has been used with horizontal grid resolutions of 18 km (nest 1),6 km (nest 2) and 2 km (nest 3). Vertically the model extends up to a pressuresurface of 100 hPa (about 16 km), 23 layers have been used to resolve the verticalstructures of the atmosphere, about 15 layers are below 3000 m, the lowest layer isabout 40 m thick.

Figure 9 shows the NOx and ozone concentration as simulated for the lowestlayer of the nest-3-model together with the chemical net production rates for ozonein the lowest layer and for an altitude region of 310–430 m for 20 July 1998,14 UTC. In Figure 10 a comparison with NOx and ozone measurements made atthe surface and in 324 m height at the Frohnau Tower is shown. The site FT, locatedin the northern part of Berlin, is selected to illustrate the model’s performance withrespect to NOx and ozone. The plume of Berlin is clearly present in the NOx-concentration fields (Figure 9). Parts of the plume, however, evidently have left thenest 3 already. Southward of Berlin also areas with enhanced NOx-concentrationscould be found, probably due to air masses originating from the highly populated


Figure 10. Intercomparison of ozone measurements and EURAD simulations at site FrohnauTower in two heights at the northern city border of Berlin for 20 July 1998. CG (motherdomain), 54 km grid; N1 (nest 1), 18 km grid; N2 (nest 2), 6 km grid; N3 (nest 3), 2 km grid.

and industrialized regions in Saxony. With respect to ozone increased concentra-tions between 65 and 70 ppb are found northward from Berlin, but even higherconcentrations above 70 ppb near the southern boundaries of the nest 3 area. Thespatial pattern of the chemical net production in the near-surface layer is clearlydominated by the emissions. Ozone is destroyed in the city of Berlin and along thehighways, i.e., in the areas with high emission rates. Ozone net production of morethan 8 ppb h−1 is found northward (downwind) from Berlin and near the southernboundary of nest 3. In elevated layers ozone net production of more than 2 ppbh−1 is found throughout the nest 3 domain. Areas of major ozone net productionof more than 4 ppb h−1 are found in elevated layers downwind of Berlin and againnear the southern boundary of the innermost nest.

3.3.2. Process Studies with KAMM/DRAIS

A stand-alone version of the model system KAMM/DRAIS was used to simulatethe spatial and temporal distribution of the atmospheric variables and the concen-trations of the relevant chemical species of the BERLIOZ case 20 July 1998. Thewhole model system runs in a fully coupled mode that means all physical andchemical processes are calculated within one model run and the physical para-


meterisations are identical in the meteorological and chemical transport part. Thehorizontal grid size used for this simulation is 2 km. Stand alone version means thatno nesting procedure was applied but the simulations were initialised and driven asfar as possible by observations of BERLIOZ. A description of the model system isgiven in Vogel et al. (1995), details of the set up of the model and the input datacan be found in Hammer (2001). The results of these simulations serve as a basecase for further investigations. Especially, Sillmans (1995) indicator concept whichallows a separation of the different photochemical regimes (NOx versus VOC sen-sitivity) is applied and improved. These investigations have been published in aseparate paper (Vogel et al., 2001).

Figure 2 shows the simulated wind field at 16 m above surface at 07 UTC and15 UTC together with the observations. It has to be mentioned that the observedwinds were measured between 4 and 10 m with the exception of the tower atFrohnau (324 m). However, the observed and the simulated winds show a pro-nounced turn of the wind direction between 07 and 15 UTC from south-easterly tomore southerly winds.

The model results for 20 July are used for detailed process studies. Figure 11shows the spatial distribution of the temporal change (�chemO3) of the ozone con-centration caused by chemical reactions for the time interval 13 to 14 UTC at about280 m above surface.

This temporal change is calculated from:

�chemO3 = 1�t

∫ t+ �t2t− �t2

P(O3, t′) − L(O3, t ′) dt ′ (3)

with δt = 1 h. P(O3) and L(O3) are the modelled local chemical production andloss of ozone, respectively.

Negative values of �chemO3 are found at the locations of single sources andin a larger area in the north-western part of Berlin and are caused by fresh NOemissions. Positive values up to 6 ppb h−1 are found in the lee of the single sourcesand in the lee of Berlin. In addition Figure 11 depicts the projection of the DO 128flight pattern between 13 UTC and 16 UTC. Comparing these results with those ofthe EURAD model (Figure 9) it is obvious that similar absolute values of �chemO3are found with the two different models.

Since, for the first time we were able to derive the local chemical ozone netproduction from observations along a flight pattern it is now possible to make adetailed comparison with the model results.

Figure 12 shows measured and calculated O3 concentrations along the DO 128flight pattern. The modelled data are produced by a spatial and temporal interpola-tion of the model results to the actual position of the aircraft in space and time. Acomparison of the measured and the modelled ozone concentration shows that themodel reproduces the main features. However, differences in the order of 5 ppb arefound.


Figure 11. Horizontal distribution of �chemO3 at 13:30 UTC at 280 m above surface. Inaddition the DO 128 flight pattern and the locations of surface stations with chemical data areshown.

In addition Figure 12 shows the modelled �chemO3 along the flight pattern ofthe DO 128. Again a spatial and temporal interpolation of the model results is car-ried out. With two exceptions, which are caused by strong single sources, positivevalues of �chemO3 are found. The values vary between 3 and 6 ppb h−1. In general�chemO3 is decreasing with time due to decreasing solar radiation.

According to the process studies based on the observations in section 3.2.1averaged values of �chemO3 were calculated for different flight sections (windward,city, lee; Figure 12). These averaged values are indicated by 〈�chemO3〉. Table IVallows a comparison of 〈�chemO3〉 and the measured chemical net O3 productionfor different flight sections and flight levels. The deviations given in Table IV areestimated errors in case of the observations and standard deviations within thespecific flight sections in case of the model results. We found that the model resultsand the observations are in the same order of magnitude. However, even qualitativediscrepancies are obvious. While the highest values of the measured chemical netO3 production are observed in the lee sector such a pronounced maximum is notfound in the modelled 〈�chemO3〉. Figure 11 shows the reason for this discrepancy.In the lee sector the flight path goes through a local minimum of the modelled�chemO3 and in the windward sector it passes a local maximum of the modelled�chemO3. If we would turn the modelled distribution only by a few degrees to the


Figure 12. Height above NN (top), measured and simulated O3 (middle) and simulated�chemO3 (bottom) along the DO 128 (IBUF) flight pattern of 20 July 1998.

left, which might be justified by knowing that there is a bias of calculated andobserved wind directions, we would find modelled �chemO3 of about 3–4 ppb h−1in the windward sector and of more than 6 ppb h−1 in the lee sector. This findinghighlights the difficulties which are connected with an objective assessment of nu-merical models and demonstrates, why useful objective methods for the validationof simulated concentration distributions are still missing.


4. Summary

The influence of regional anthropogenic precursor emissions on the ozone concen-tration downstream the source area is investigated in this paper. Characteristics ofthe city-plume are:

• The large scale ozone distribution is modified in the local and regional scaleby anthropogenic precursor emissions especially from large urbanized areas.A local increase of the ozone concentration from 70 to 85 ppb is found in thiscase.

• Due to chemical reactions the maximum ozone concentrations are found –as predicted by CTMs – far in the lee of the source area, about 30 to 70 kmdownstream. Near the city the ozone concentration is unchanged.

• Within the city-plume a striking microstructure of the ozone distribution isdetected caused by local sources and meteorological processes.

The processes involved in the city-plume formation are analysed in detail:

• The contributions of advection, turbulent diffusion and chemical net produc-tion are, although different calculation schemes are used, in the same order ofmagnitude of ±8 ppb h−1. In most cases they are between ±2 and 6 ppb h−1.So compensation of the processes is obvious.

• Before noon turbulent diffusion governs the local ozone increase near thesurface. At noon chemical net production leads to a significant increase ofozone in the plume far in the lee.

• The chemical net production of ozone in the plume caused by the regionalemissions is rather low. It is between 5 and 21 % of the large scale contributionin the cases of this study.

The measurements are compared with CTM results:

• The KAMM/DRAIS model, driven by measured wind and temperature pro-files, calculates the local change of ozone concentration in different heightsupstream and downstream of Berlin. The offset between measurement andsimulation is max. 5 ppb. This is a mean difference of 7.5% if the mean mixingratio is 67.5 ppb.

• KAMM/DRAIS simulates the chemical net production of ozone (2.7 to4.7 ppb h−1) with realistic microstructure and in the same order of magnitudeas the measurements are.

• EURAD – using a nesting algorithm – solves regional and local processesdown to 2 km resolution in the city-plume and predicts a chemical netproduction rate of 4.0 to 6.0 ppb h−1 as it is measured in the plume.


Acknowledgements

We thank all co-workers involved in the BERLIOZ campaign and in the evalu-ation and interpretation of the data. We gratefully acknowledge the support ofthe project by the authorities of Berlin and Brandenburg. Special thanks to theGerman civil aviation authority, DFS, which supported the research flights in theBerlin air space and made even unusual flight requests possible. The airborneprocess studies were made possible by the crews of the Dornier 128 from theTechnische Universität Braunschweig, from the MetAir Dimona and from theCessna 402 C. Thanks also to V. Mohnen and H.-J. Kanter for quality assessmentof the chemical and meteorological measurements. The work was supported by theGerman Ministry for Education and Research (BMBF) as a part of the program‘Troposphärenforschung’.

References

Affre, Ch., Carrara, F., Lefebre, F., Druilhet, J., Fontan, J., and Lopez, A., 1999: Aircraft mea-surement of ozone turbulent flux in the atmospheric boundary layer, Atmos. Environ. 33,1561–1574.

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Documents

Ozone and PAN Formation Inside and Outside of the Berlin ...easd.geosc.uh.edu/rappenglueck/pdf/2002_corsmeier_et_al_JAC.pdfDuring BERLIOZ in July/August 1998 in Berlin and Brandenburg,