Impacts of Meteorological Conditions Modified by Urban Expansion on Surface Ozone

over Yangtz River Delta and Pearl River Delta region, China  

Xuemei Wang, Ziwei ChaiDept. of Environmental Sciences, Sun Yat-Sen University, China

Fei Chen, Christine Wiedinmyer, Alex Guenther, Mukul TewariNational Center for Atmospheric Research, Boulder, CO, USA

6th Annual CMAS Conference October 1st,2007

Outline

• Regional Air Quality IssuesRegional Air Quality Issues

• Meteorological conditions modified

by urban expansion

• Impacts of urban expansion on Impacts of urban expansion on

surface ozonesurface ozone

• Summary

Satellite View Alerts China to Soaring Pollution (GOME and SCIAMACHY)

(Richter et al., Nature, Sept 1, 2005)

NO2 (vertical column)

NO2 (1996 - 2004)

Yangtze River Delta/ Shanghai Region

(YRD)

Pearl River Delta Region (PRD)

2001 2002 2003 2004

Spring

Summer

Autumn

Winter

Atmospheric Opitcal Depth(AOD)

Rapid Urban Expansion in PRD and YRD, China

1993

1993

2002

2002

PRD Area = 41700 km2, Population: 1986~20million, 2005 > 45 million

YRD Area= 95225 km2, Population: 1986~30million, 2005 > 60 million

2004-6-30 2:57am

Consequences of rapid urbanization

more pronounced urban heat islands (UHI)

more surface emission in PRD

0. 0100. 0

200. 0300. 0400. 0

500. 0600. 0700. 0

800. 0900. 0

NOx SO2 VOC

Emis.(KTon/year)

1997 2003

Impacts of Meteorological Conditions

Urban heat islands reduce the strength of nocturnal land-breeze (return flow from land to sea), so air

pollutants tend to accumulate over land.

 Lo, J.C.F., A.K.H. Lau, F. Chen,J.C.H. Fung, and K.K.M. Leung, 2007 (J. Appli. Meteorol. And Climate)

WRF-Chem 12-km Simulation and Configuration

WRF-CHEM model configuration

WSM 5-class microphysics Kain-Fritsch cumulus

Dudhia scheme short wave RRTM longwave radiation

Yonsei University (YSU) (PBL) Noah land surface scheme

Urban Canopy model (UCM) Fast-J radiation scheme

RADM2/SORGAM (gas+ aerosol)

Initial and Boundary conditions

1-degree FNL for meteorology 6-min resolution emission inventory

TRACE-P observation data for chemistry

Simulation March 2001

Topographical height (m)

Evaluation of WRF-Chem Met. Simulation

Compared with NCEP analysis data, WRF monthly averaged 2-m

temperature and wind direction have the same pattern,

but with higher wind speed in YRD

Evaluation of WRF-Chem Simulated

Concentration

Simulations from two WRF-Chem packages have similar trend

Urbanization Increases both Day- and Night-time 2-m Temperature

Simulation Urban - Simulation PRE-Urban averaged for March 2001

PRD has smaller increase of 2-m temperature than YRD

YRD

PRD

Urbanization Decreases both Day- and Night-time 10-m Wind Speed

PRD has larger decrease of 10-m wind speed than YRD, and daytime reduction in wind speed is larger than that for nighttime

Urbanization Decreases both Day- and Night-time 2-m Water Mixing Ratio

PRD has larger decrease of 2-m water mixing ratio than YRD, and daytime reduction in Q2 is larger than that for nighttime

Urbanization Increases both Day- and Night-time Boundary Layer Depth

PRD has smaller increase in PBL depth than YRD

Urbanization Increases Surface Ozone

Concentration

Urbanization increases surface ozone (more for nighttime) PRD has larger increase than YRD

Differences in 10-m wind and O3

between Urban and Pre-urban

Urbanization enhances the convergence, especially in the PRD. Daytime convergence is weaker than that for nighttime

Relative O3 change (ppbv) and relative 10-m wind difference

Daytime Nighttime

Summary • Impacts of urban expansion can modify surface and

PBL structures:– increase temperature and decrease wind speed – PBL depth increase more in the day time than that in the

night time.

• Comparing PRD and YRD (cities clusters with different urban distribution and located in different climate regimes), PRD has – smaller increase of 2-m temperature than YRD– larger decrease of 10-m wind speed than YRD– smaller increase of PBL depth than YRD– larger increase of surface ozone than YRD.– larger decrease of 2-m water mixing ratio than YRD

• Dynamic and thermal effects of urbanization all have impacts on surface ozone.

Thank you !