Impacts of weather conditions modified by urban expansion on surface ozone: Comparison between the Pearl River Delta and Yangtze River Delta regions

Xuemei Wang,Zhiyong Wu,Fei Chen,Meigen Zhang,Alex Guenther,Christine Wiedinmyer,Mukul Tewari

doi:10.1007/s00376-009-8001-2

Abstract

In this paper, the online weather research and forecasting and chemistry (WRF-Chem) model is used to explore the impacts of urban expansion on regional weather conditions and its implication on surface ozone concentrations over the Pearl River Delta(PRD) and Yangtze River Delta(YRD) regions. Two scenarios of urban maps are used in the WRF-Chem to represent the early 1990s (pre-urbanization) and the current urban distribution in the PRD and the YRD. Month-long simulation results using the above land-use scenarios for March 2001 show that urbanization increases both the day- and night-time 2-m temperatures by about 0.6°C and 1.4° C, respectively. Daytime reduction in the wind speed by about 3.0 m s−1 is larger than that for the nighttime (0.5 to 2 m s−1). The daytime increase in the PBL height (> 200 m) is also larger than the nighttime (50–100 m). The meteorological conditions modified by urbanization lead to detectable ozone-concentration changes in the PRD and the YRD. Urbanization increases the nighttime surface-ozone concentrations by about 4.7%–8.5% and by about 2.9%–4.2% for the daytime. In addition to modifying individual meteorological variables, urbanization also enhances the convergence zones, especially in the PRD. More importantly, urbanization has different effects on the surface ozone for the PRD and the YRD, presumably due to their urbanization characteristics and geographical locations. Even though the PRD has a smaller increase in the surface temperature than the YRD, it has (a) weaker surface wind speed, (b) smaller increase in PBL heights, and (c) stronger convergence zones. The latter three factors outweighed the temperature increase and resulted in a larger ozone enhancement in the PRD than the YRD.

Highlights

Changes in land use and land cover (LULC) alter the exchange of energy, momentum, moisture, and other trace gases within the vegetation-soilatmosphere continuum, subsequently affecting the global and regional climate (Charney et al, 1977; Chase et al, 1996; Foley et al, 2005), and impacting the dispersion of pollutants and air quality
In Pearl River Delta (PRD), cities are connected with each other and form a city cluster; in Yangtze River Delta (YRD), the urban expansion and clustering of surrounding towns and counties are located in centralized cities, like Shanghai and along the Ningbo-Shanghai-Hangzhou transport passageway Yao and Chen (1998)
The main objective of our study is to use the weather research and forecasting with online chemistry (WRF-Chem) model to conduct month-long simulations to examine the degree to which urbanization-induced weather conditions impact surface ozone in highly-urbanized regions located in slightly different climate regions: the PRD and YRD

Summary

Introduction

Changes in land use and land cover (LULC) alter the exchange of energy, momentum, moisture, and other trace gases within the vegetation-soilatmosphere continuum, subsequently affecting the global and regional climate (Charney et al, 1977; Chase et al, 1996; Foley et al, 2005), and impacting the dispersion of pollutants and air quality. Urban areas account for 60% in the total land cover in NO. The expanded urban areas in these two districts were generally converted from farm lands. The PRD region, an area of about 41700 km, located in the southern part of the Guangdong Province, includes mega-cities such as Hong Kong, Guangzhou, Shenzhen, and seven other mid-size cities. The YRD region with area of 109600 km is located in east-central China, which includes the Jiangsu Province, Shanghai, the Zhejiang Province, and a part of the Jiangxi Province and the Anhui Province. In PRD, cities are connected with each other and form a city cluster (see Fig. 1d); in YRD, the urban expansion and clustering of surrounding towns and counties are located in centralized cities, like Shanghai and along the Ningbo-Shanghai-Hangzhou transport passageway Yao and Chen (1998)

Objectives

Methods

Results