Using a mobile laboratory to characterize the distribution and transport of sulfur dioxide in and around Beijing

M. Wang,W. W. Lin,Z. F. Wang,Y. Li,Q. H. Zhang,T. Zhu,J. P. Zhang

doi:10.5194/acp-11-11631-2011

Abstract

Abstract. Megacities are places with intensive human activity and energy consumption. To reduce air pollution, many megacities have relocated energy supplies and polluted industries to their outer regions. However, regional transport then becomes an important source of air pollution in megacities. To improve air quality before and during the 2008 Beijing Olympics, a wide range of control strategies were implemented, including the relocation of polluting industries. High sulfur dioxide (SO2) concentrations were occasionally observed during this period. Potential sources from southern regions of Beijing were indicated by backward trajectories model and urban/rural stationary measurements, but direct evidence was lacking. Here we used a mobile laboratory to characterize the spatial distribution and regional transport of SO2 to Beijing during the Campaign for Air Quality Research in Beijing and the Surrounding Region (CAREBEIJING)-2008. Among the five days chosen for the case studies during the Olympic air pollution control period, four had high SO2 concentrations (6, 20 August and 3, 4 September 2008) while one had low SO2 concentration (11 September 2008). The average values of SO2 during the low SO2 concentration day were 3.9 ppb, much lower than during the high concentration days (7.8 ppb). This result implied an impact by regional transport from outside Beijing. During these days, we captured transport events of SO2 from areas south of Beijing, with a clear decrease in SO2 concentrations southeast of the 6th to 4th Ring Roads around Beijing and along the 140 km highway from Tianjin to Beijing. The influx of SO2 through the 4th to 6th Ring Roads ranged from 2.1 to 4.6 kg s−1 on 4 September and 0.2 to 1.6 kg s−1 on 20 August 2008. The differences of influx in days were due to the variations of emission changes, transport directions and dilutions. Locally emitted SO2 from a source located along Jingshi Highway outside the southwest section of the 5th Ring Road of Beijing was identified using wind field data generated by the Weather Research and Forecasting model and the measured particle size distribution, with an estimated flux of 0.1 kg s−1 to Beijing. Estimated uncertainties for SO2 influx were approximately 31%.

Highlights

Sulfur dioxide (SO2) is one of the most important precursors of secondary aerosols in the atmosphere
SO2 concentrations were low during the Olympic air pollution control period (8 to 24 August 2008) at all stations, with average values of 5.8 ppb in the city and 3.2 ppb in rural areas
During the 2008 Beijing Olympics period, most of the SO2 emission sources were strictly controlled within and around Beijing (Wang et al, 2009a) and the reduction of SO2 was estimated to be about 47 % compared with the days before the Olympics; we assumed that local emission within Beijing city was not a major source of the increase in SO2

Summary

Introduction

Sulfur dioxide (SO2) is one of the most important precursors of secondary aerosols in the atmosphere. It is responsible for severe air pollution, leading to degraded visibility, changes in the radiation budget, and acid rain (Wang et al, 2008; Zhang et al, 2004a; Ramanathan and Crutzen, 2003). Industrialization, and urbanization have occurred within and around the megacity of Beijing, increasing demands for fossil fuel consumption (Ohara et al, 2007), which is the main source of SO2. M. Wang et al.: Distribution and transport of sulfur dioxide in and around Beijing

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Conclusion