Water spray geoengineering to clean air pollution for mitigating severe haze in china’s cities. Keynote from Prof. Shaocai Yu

Water spray geoengineering to clean air pollution for mitigating severe haze in China’s cities

Shaocai Yu, Professor, Ph.D.

Research Center for Air Pollution and Health, College of Environmental and Resource Sciences,

Zhejiang University, China. 浙江大学环境与资源学院

Current Researches in my group：

1. US EPA WRF-CMAQ model and OBSto study

and forecast air pollution-haze in China

2. Water spray geoengineering to clean air

pollution

3.Air pollution and environmental health

1。， WRF-CMAQ空气质量模式研究中国东部区域大气污染和雾霾演变规律及其动态预警预报

Meteorological Model

WRF modeling System:

Δx=12 km, 4km

34 layers

Land-Surface: PX LSM PBL: ACM2 Cloud Physics: Morrison Cumulus: Kain-Fritsch, not for 4km Shortwave: RRTMg, or CAM Longwave: RRTMg, or CAM

Coupler 双向耦合器

Chemical Transport Model CMAQ Modeling System: Photochemistry: CB05

59 organic and inorganic species, 156 chemical reactions

Aerosol module: AE6

3 lognormal modes, organic and inorganic Emission: SMOKE

In-line emission for biogenic species

AQPREP Prepares virtual CMAQ compatible input met. files

CMAQ-mixactivate: cloud drop, ice number conc. Direct forcing: Aerosol size, composition, conc.

WRF模式

CMAQ模式

US EPA Two-way coupled WRF-CMAQ modeling System (Interaction and feedback) (Yu et al., 2014)

1. Model domain for studying and forecasting air pollution

On 1/7/2014, published in《Environ Chem Lett》

The Springer had a Press Release for this paper in English, Chinese and German, More than 600 world medias, newspapers, and TVs have widely reported the results Such as sciencedaily, natureworldnews, pbs, IBtimes, CNN, Wall Street Journal, usa.chinadaily, Hongkong Herald, SouthChina Morning Post, and Chinese Academy of Science, eastday, sina, Shanghai people's Broadcasting Station etc

Background（Air pollution and haze formation)

v Main emission sources in China： v Industrial: point sources, coal-combustion is mainly

responsible for air pollution in China

v Personal activities: traffic, heating, cooking, v Biogenic emissions： area sources

v As a city, emissions: ü Local sources： controllable ü Long-range Transport：uncontrollable

Background (emission sources in China)

Air pollution is not easy to manage because of this nature

Backgound（How USA controls air pollution)

vLos Angeles Photochemic. Smog Event (Aug-Sep., 1955) vHourly O3con. >500 ppbvMain reason: car emissionsvControlling car emissions improves air quality significantly

Haze problem is still big right now (2011)

v1948 Pittsburgh Donora smog event：vkilled 20 people and sickened 7,000vPittsburgh: capital of the iron and steel industryvEmissions in Donora ： U.S. Steel industry (Zinc)

Significantly improve air quality method now:Shut down the polluting enterprises, enterprise transformation, especially high-tech industry.

Backgound (How USA controls air pollution)

Background (air pollution in USA)

vAir pollution and haze in Utah’s valley, Salt Lake City

vMost serious air pollution city in USA。vJanuary 25, 2014: Largest Air Pollution Rally in US History in Utah's Capitol Hill vSources: Copper industrial and car emissionsvPM2.5>150 µg/m-3

Air pollution is serious because the industrial emissions are still there！！！

背景（英国London治理大气污染现状）vLondon Great Smog event（1952）

vCauses：Coal combustion

vControl method:vClean air law for London.vShutting down all power plants and industrial facilities in London. The massive transformation of traditional stoves, reducing coal use, central heating, improvement of city public traffic system.

In both USA an UK, Shutting down polluting industrials is main reasons for the significant improvement of air pollutions

Background (air pollution control in China)

vControl strategy：vSeptember 2013，State Council issued <<Action Plan for the Prevention and Control of Air Pollution>>

vThis plan aims to reduce air pollution by over 10% from 2012 to 2017

vTechnology： Direct emission reduction and regional joint prevention and controlvIn Beijing：four methods: Reducing coal use and emissions, controlling dust and car

vHowever, from 2013 to now, all these measures have not achieved significant results (Xinhua)!!

v 2014-03-26 PM2.5 conc. , v Beijing had yellow warning for heavy haze (03-24）

03-26 AQI in Beijing: 400 Provincial Coal Consumption

v Surface weather map (http://www.nmc.gov.cn/publish/observations/weatherchart-h000.htm)

Beijing: Low pressure system，poor dispersion conditions

L L

L March25

L

Cold Front

0：00 6：00

12：00 18：00

vThe air Pollution Control during Beijing Olympic GamesvThe city suspended 50% vehicles, Shut down steel Corporation and other 21 key polluting enterprises

vSO2, NOx, NMVOC emissions reduced by85%， 46%，57%

vSix provinces: air pollution joint prevention and controln “APEC Blue” in Beijing (2014 Fall)

n widely credited to temporarily shutting down hundreds of factories in cities in Beijing and surrounding six provinces

Air quality improvement mainly due to shutting down polluting factories and stop driving, instead of direct emission reduction by

technology!!



vEmergency plan for heavy air pollution days

vBeijing: week haze from 2/20-27 (2014)(PM2.5>200 µg/m3)v《Beijing's Heavy Air Pollution Emergency Plan》：

vShut down 58 enterprises; reduce 30% production in 41 factories etc

vAll emergency plans are used, no obvious effectvFinally on the 27, haze disappeared because of wind and rain

vWhy？vAir pollutants are already in the atmosphere, all emergency can only reduce emissions, but there is no effective way to remove pollutants in the atmosphere !!Haze was removed by Nature (wind and rain), no other way (Xinhua)

Background (air pollution control in China)vRemoval of pollution in the air (Yu et al. 2000; 2001)

vWet deposition:vFalling rain droplets or snow particles scavenge aerosols

vBrownian diffusion, interception, impaction and turbulent diffusion

vEffective way to remove particles and trace gasesvDry deposition

vAerosols and other acidic substances directly deposit to the surfacevWind speed, atmospheric stability, chemical and surface characteristics

These are scientific basis for removing haze by rain and wind,

Wet dep. is more efficient for removing air pollutants

Background (air pollution control in China)v Recent very good air quality in China

Precipitation in China on 5/13 14:00-5/14 14:00

PM2.5 in China on 5/14 14:00

Rain causes good air!!!

Water spray geoengineering to clean air pollution for cities

v Inspiration ： v Wet dep. is the most effective method to clean haze v spray water into the atmosphere like watering a garden v Shanghai with a big river has heavy haze

Shanghai can use water spray geoengineering to curb its

haze and air pollution

1/23/2013

v Rivers and lakes accounted for 8% areas in Hangzhou. Qian Tang River passes through the city.

Water spray geoengineering to clean air pollution for cities

Hangzhou can use water spray geoengineering to curb its haze and air pollution

v PM2.5 concentrations (CPM2.5) with precipitation scavenging time can be calculated as follows (Seinfeld and Pandis, 2006)：

CPM2.5=C0，PM2.5e

-µt

C0，PM2.5：initial PM2.5 concentration µ：precipitation scavenging coefficient(hr-1) t:scavenging time(hr)

Water spray geoengineering to clean air pollution and haze（Yu, 2014)

PM2.5 conc. as a function of scavenging time for different scavenging coefficients

PM2.

5con

cent

ratio

n

Scavenging time (hr)

scavenging coefficient µ(hr-1)


Scavenging time needed (h) to decrease PM2.5 conc. from three original PM2.5 conc. to 35 µgm-3

PM2.5 (µg m-3) µ(hr-1) 100 200 1000

0.01 105.0 174.3 335.2 0.05 21.0 34.9 67.0 0.1 10.5 17.4 33.5 0.5 2.1 3.5 6.7 1 1.0 1.7 3.4

1.5 0.7 1.2 2.2 2 0.5 0.9 1.7

2.5 0.4 0.7 1.3 3 0.3 0.6 1.1


v Precipitation scavenging coefficient µ(hr-1) (Pruppacher and Klett, 1997):

da: aerosol particle diameter Dr: raindrops diameter E(Dr, da) is collection efficiency, P is precipitation rate (rainfall intensity).


v Precipitation rate, particle and drop sizes determine scavenging coefficient

Scav

engi

ng c

oeff

icie

nt(h

r-1)

Par$cle diameter(um)

Droplet size

Automatic sprinkler system need to be specially designed to spray droplet size and rain strength



Charged drops increase scavenging coefficients

A. K. BARLOW and J. LATHAM,A laboratory study of the scavenging of sub-micron aerosol by charged raindrops, Quart. J . R. Met. SOC. (1983), 109, pp. 763-770

Ø Charged drops increase E by two orders Ø PM2.5 particles have positive charges

Collection coefficient

Charge

Charge-free drop

Charged drop

Air assisted electrostatic spray gun

Ø Droplet diameter with charges: 100-300 µm, Price: 50,000RMB

Ø Shot range: 20 -100 meters

Conceptual pictures of the water spray geoengineering

v For cities water sprinklers are installed on the roof of buildings (and tower)

v For the open place, build towers

v  This can apply to industrial areas。


Water cost estimates: Ø Beijing City area: 16,801km2, Ø  a sprinkler for every 250 m,

Ø  total 268816 sprinklers Ø A sprinkler sprays 7.6 Tons/day。Price: 1ton/4yuan Ø Electricity for bring 1 ton water to 50 m high: 0.095yuan。 Ø  1 spray point fee: 31.1yuan/day

Ø  Fee for 268816 spray points: 8,366,214yuan Ø Assume that 300 days is needed, fee: 2.51billion yuans/year Ø  If the water can be collected with 50% efficiency, fee

Ø  1.26billion yuan/year


The arguments in favor of this engineering approach:

(1)Precipitation scavenging processes are natural processes。 (2) Speed of action: precipitation scavenging management can work quickly because the precipitation scavenging can remove air pollution within half hour 。

(3)Technological feasibility: all technologies and material required are pre-existing: high building, high tower, water, automatic sprinkler head to spray water etc.

(4)Low cost issue: the low-tech nature of this engineering approach has led us to believe that it will have low cost

(5) Efficacy: (6) Some tipping points：remove other gaseous pollutants such as SO2 and Nox, reduce possible O3 and secondary PM formation and clean the streets of the megacities。


For possible potential problems: (1)If too much water is sprayed into the atmosphere at one time and one place, this will cause flood as we can expect. (2)If water droplets do not reach ground but evaporate completely during the falling, this will increase the relative humidity in the atmosphere in the megacities. (3) If water is sprayed into the atmosphere in the cold days such as winter time, this will produce snow and cause slipping grounds because of freezing rain.


Definitely, there are still significant challenges in designing a specific delivery system that is capable of delivering water in the right manner, right place and right time to encourage most effective precipitation scavenging for air pollution and how to set up the sprinkler systems for a city to mitigate the regional haze with low cost

Research Question for water spray geoengineering


South China Morning Post (HongKong)： "We will do some tests in Zhejiang University campus first and then Hangzhou city if everything goes well," he says. "If we are successful, our work can be followed by the other cities in China and around the world."

Prospects:


Ø  It will take ten years or longer to realize the effective management of the haze through direct control of air pollutant emissions as governments say,

Ø  Under the condition with no big change in the energy structure and current emission situation in China,

I think the water spray geoengineering may be effective emergency scheme for mitigating serious haze pollution in China.

Prospects Water spray geoengineering to clean air pollution and haze（Yu, 2014)