Concentration and chemical composition of PM_2.5 in Shanghai for a 1-year period

Abstract

Weekly PM_2.5 samples were collected in Shanghai, China at two sites, Tongji University and Hainan Road. Sampling started in March 1999 and was conducted for 1 year. The ambient mass concentration and chemical composition of the PM_2.5 were determined. Chemical analyses included elemental composition, water-soluble ions, and organic and elemental carbon. Weekly PM_2.5 mass concentrations ranged from 21 to 147 μg/m³, with annual average concentrations of 57.9 and 61.4 μg/m³ at the two sites, respectively. Seasonal variation of PM_2.5 concentrations was significant, with the highest concentrations observed from mid-November through December and the lowest from June through September. Ammonium sulfate and nitrate accounted for 41.6% of the PM_2.5 mass with sulfate alone accounting for 23.4% of the PM_2.5 mass. Carbonaceous material accounted for 41.4% of the PM_2.5 mass, with 73% of that mass being organic, as defined by the TOR analysis method. Crustal components averaged 9.6% of the PM_2.5 mass. Potassium, which was 95% water soluble, accounted for 2.7% of the PM_2.5 mass.

Introduction

Air quality is an important issue in China and the Chinese government is committed to improving it by establishing more stringent emission control strategies. Particulate matter is a primary concern due to its possible health impacts and visibility degradation. China has a PM₁₀ standard, but does not have one for PM_2.5. Thus, relatively little data is available concerning PM_2.5 concentrations and trends. In 1999, we initiated a PM_2.5 monitoring program in Beijing and Shanghai that included chemical characterization of the collected PM. Results from the first year of monitoring in Beijing have been reported (He et al., 2001). This paper examines the results from 1 year of monitoring in Shanghai.

Shanghai is the largest city of the Shanghai Municipality, which has over 15 million people. It is located at the mouth of the Yangtze river in Jiangsu province and is one of the worlds’ largest seaports. It has a strong commercial and industrial base with China's largest petrochemical complex, its largest steel output, and other major industries. Years of rapid economic growth and urban development have burdened its air quality, resulting in visibility reduction and public health concerns (Ye et al., 1999; Brunekreef and Dockery, 1995; He et al., 1993; Shen et al., 1992; Yan, 1989). In addition to local air quality problems, there are also regional concerns. For example, the impact of atmospheric haze on agriculture due to reduced sunlight was assessed for the lower Yangtze basin with an estimated 5–30% reduction in crop yields (Chameides et al., 1999). Xu (2001) suggested that the “northern drought with summer flooding”—a recent climatic change phenomenon in China during the last 20 years may be attributable to increases in sulfur dioxide emissions from the industrialization of east China. Despite these serious concerns, there is little published data on atmospheric PM concentration, composition, and sources. Song and Cui (1996) did make total suspended particles (TSP) and SO₂ measurements in Shanghai and four other cities in China under a UNEP-WHO environmental program over a 12-year period. It was observed that the TSP mass concentration was in the 100–300 μg/m³ range with the highest concentration in the winter. Recently, Davis and Guo (2000) measured PM₁₀ in Shanghai on two separate days and reported the mean geometric particle diameters to be 1.2 and 1.6 μm.

Increased energy consumption from the 1980s to the early 1990s has contributed to the increasing ambient aerosol concentration in Shanghai. According to Tong and Xi (1995), more than 80% of the energy in Shanghai was from low quality coal. The industrial consumption of coal was expected to rise from 19.6 million tons in 1989 to 41.7 million tons in 2000. Further examination of the SO₂ emissions led them to suggest that energy consumption has to shift from the use of coal for power generation to lower sulfur fuel oil or natural gas to improve air quality. Chang et al. (1998) modeled the air quality in Jiangsu province and concluded that the atmospheric SO₂ burden represented a significant health risk to Shanghai. Flue-gas desulfurization (FGD) for power plants and other large coal users was recommended as one key strategy to manage air quality in the region. Similar findings and conclusions were documented by Song and Cui (1996) who reported annual average concentrations of TSP and SO₂ in Shanghai and four other Chinese cities in a 12-year study from 1981 to 1992. More recently, Streets et al. (1999) emphasized the need to deploy advanced technology to control SO₂ emissions from stationary sources. They concluded that without additional controls much of the population will be exposed to SO₂ and sulfate ambient concentrations in excess of World Health Organization guidelines.

There is also concern over mobile source emissions. Ye et al. (1999) noted that mobile sources are increasing rapidly in China and that there are approximately 700,000 cars and 500,000 scooters on the streets of Shanghai. Zhou and Ye (1998) also collected particulate emissions from diesel engines, 2-stroke motorcycles and scooters and reported on the short-term mutagenic activities of the extracts. Meanwhile, Ji et al. (1993) estimated that 12,300 tons of road dusts were re-entrained into the ambient air in Shanghai annually, which is about 8% of the stationary source inventory. It is expected that continued urban development will cause further increases in population and traffic density for the next 30 years.

The purpose of this work was to conduct weekly monitoring of PM_2.5 to examine seasonal variations in the PM_2.5 and gases, and to determine the composition of the PM in an effort to better understand its sources.