Simultaneous measurement of particulate and gaseous pollutants in an urban city in North China Plain during the heating period: Implication of source contribution

摘要

A comprehensive measurement program was undertaken in winter 2009 in a large urban city (Ji'nan) in North China Plain (NCP). The average concentrations of NO, NO_2, NO_x, NO_y, SO_2,O_3, CO, PM_(2.5) and BC during the program were 63.9 ± 65.1 ppb, 45.2 ± 16.9 ppb, 106.6 ± 77.8 ppb, 120.7 ± 77.4 ppb, 54.3 ± 25.8 ppb, 6.3 ± 6.0 ppb, 2138.3 ± 1512.8 ppb, 171.3 ± 83.9 μg/m~3 and 9.8 ± 6.9 μg/m~3, respectively. Two severe haze episodes were observed. All species, except O_3, had elevated concentrations on the episodes compared with those on non-hazy days due to accumulation of pollutants. Diurnal variations of species concentrations and correlation analysis suggested that emissions from vehicles and coal combustion (from power plants, industry and domestic heating) are the main sources. Air mass on Episode 1 was predominately influenced by coal combustion, while pollution was characterized by the vehicular emissions on Episode 2. In contrast, on non-hazy days, pollutants were mainly from the mixing of local coal-fired and vehicular exhaust emissions. These distinct characteristics were further supported by higher ratios of CO to NO_y and SO_2 to NO_y on Episode 1 (25.46 ppb/ ppb and 0.51 ppb/ppb) compared to Episode 2 (15.55 ppb/ppb and 0.36 ppb/ppb) and non-hazy days (18.15 ppb/ppb and 0.45 ppb/ppb). Multiple linear regression analysis was applied to the concentrations of NO_y, SO_2 and CO in the observation and empirical equations were obtained for the NO_y concentration. Based on the equations, the relative contributions from mobile (i.e. vehicular exhaust) and point sources (i.e. coal combustion) to NO_y were estimated to be 68.2% and 38.6%, respectively, demonstrating that even in the demanding period of domestic heating in NCP, vehicular emissions in a large urban city contribute more to NO_y than coal combustion emissions. This also implies that vehicular emissions, featured with high NO_x, become a dominant source of pollution, highlighting the recent finding of long-term increase of NO_2 in the NCP region by satellite observation (Richter et al., 2005).