Characteristics of fine particle and black carbon during haze episodes in a coastal city, Xiamen China

摘要

Rapid economic development and over centralized populations in eastern coast cities of China resulted in the worse air quality. Following the dominant economic zones of Pearl River delta and Yangzi River delta, the air quality and visibility of previous pristine area of Fujian province was becoming bad and worse. In Xiamen, the haze days increased from 9 days yearly during 1956-2002 to over 70 days yearly in recent years. To characterize the black carbon and fine particle in Xiamen during haze days, organic carbon (OC) and elemental carbon (EC) of PM_(2.5) were measured during haze episodes of 2010. PM_(2.5) samples on quartz filter were collected at Hong-wen, an air monitoring station in Xiamen urban area from September to November, 2010. The PM_(2.5) concentrations were quantified and OC/EC were measured by DR12001A carbon analyzer with 1MPROVE-A method. Hazes were determined by meteorological visibility. According to the backward trajectory, the air mass generally came from the Northeast mainland or Taiwan Western Strait during this autumn. The results showed that PM_(2.5) were 28.08 - 116.15 μg/m~3 (mean 53.62μg/m~3) at normal days and 43.90-288.45 μg/m~3 (mean 96.72μg/m~3) at haze days, respectively. There was a significant correlation between OC and EC at normal days (R~2=0.94) and haze days (R~2=0.90) during September, indicated the same sources. However, there were not significant correlationships at normal days and haze days in October and November (R =0.67) (Fig.1), which indicated some complex sources for OC and EC. After calculated Secondary Organic Carbon (SOC), we found 41-44% SOC contributed to OC at normal days and 43.9- 59.9% at haze days. Due to two sand storms occurred in Neimenggu during November and diffused whole country, the haze in this autumn could be divided into three types, local pollutants-effects haze in September, mixture pollutant-effects haze in October and sand storm-effects haze in November. Comparing with other mega cities in China, OC, EC and OC/EC of Xiamen are generally lower than Peking, Guangzhou, Shanghai and Xi'an. Marine can impact on the concentration and composition of elemental carbon and general increase the black carbon input since more old carbon bound in marine aerosol. Additionally, air pollution and whether conditions have not a significant relationship with the visibility during the sampling periods. It is obviously that marine aerosol plays an important role to impact the air visibility. The assessment system of the air quality and visibility for inland cities are not suitable to seaside cities.