Abstract: The mass concentrations and mass-size distributions of the main chemical compositions in PM1 were observed from summer of 2013 to spring of 2014 in Lin’an regional background site of the Yangtze River Delta (YRD). The annual average mass concentration of PM1 was 53 mg/m³. Organics was the dominant composition, which accounted for 47% of PM1 , followed by sulfate (23%), nitrate (16%), ammonium (12%) and chloride (1.2%). The maximum mass concentration of PM1 was found in winter (84 mg/m³) and the minimum was in fall (38 mg/m³). The mass concentration of PM1 during polluted days was 24 times higher than that during clean days in winter. The nitrate increased most significantly in winter among all species as a result of increased emission of coal combustion and low temperature. The peak size of organics was lower than other compositions and the peak size of the sulfate was the largest. The peak sizes of all kinds of compositions in winter (~600 nm) were the maximum possibly owing to the accumulation of pollutants. The peak sizes of compositions in summer were lower than other seasons (400-500 nm). The averaged mass concentration of PM1 during clean days in summer was higher than that in other seasons, which was contributed by the regional new particles. Moreover, the aerosols accompanied with the photochemical smog and the ozone pollution in this region should be concerned further.

Key words: PM1, chemical compositions, mass-size distribution, seasonal variation