Simultaneous monitoring and compositions analysis of PM_1 and PM_(2.5) in Shanghai: Implications for characterization of haze pollution and source apportionment

摘要

A year-long simultaneous observation of PM_1 and PM_(2.5) were conducted at ECUST campus in Shanghai, the compositions were analyzed and compared. Results showed that PM_(2.5) was dominated by PM_1 on clear days while the contribution of PM_(1-2.5) to PM_(2.5) increased on haze days, indicating that PM_(2.5) should be given priority to characterize or predict haze pollution. On haze days, accumulation of organic carbon (OC), elemental carbon (EC) and primary organic carbon (POC) in PM_(1-2.5) was faster than that in PM_1. Humic-like substances carbon (Hulis-C) in both PM_(2.5) and PM, formed faster than water soluble organic carbon (WSOC) on haze days, hence Hulis-C/WSOC increased with the intensification of haze pollution. In terms of water soluble ions, NO_3~-/SO_4~(2-) in PM_1 increased with the aggravation of haze pollution, implying that mobile sources dominated on haze days, so is nitrogen oxidation ratio (NOR). Liquid water content (LWC) in both PM_1 and PM_(2.5) had positive correlations with relative humidity (RH) but negative correlations with visibility, implying that hygroscopic growth might be a factor for visibility impairment, especially LWC in PM_1. By comparison with multi-linear equations of LWC in PM_1 and PM_(2.5). NO_3~- exerted a higher influence on hygroscopicity of PM_1 than PM_(2.5), while RH, WSOC, SO_4~(2-) and NH_4~+ had higher effects on PM_(2.5), especially WSOC. Source apportionment of PM_(2.5) was also investigated to provide reference for policy making. Cluster analysis by HYSPLIT (HYbrid Single Particle Lagrangian Integrated Trajectory) model showed that PM_(2.5) originated from marine aerosols, middle-scale transportation and large-scale transportation. Furthermore, PM_(2.5) on haze days was dominated by middle-scale transportation. In line with source apportionment by positive matrix factorization (PMF) model, PM_(2.5) was attributed to secondary inorganics, aged sea salt, combustion emissions, hygroscopic growth and secondary organics. Secondary formation was the principle source of PM_(2.5). Furthermore, the contribution of combustion emissions to PM_(2.5) increased with the intensification of haze pollution, which was just opposite to hygroscopic growth, while that of secondary formation kept quite stable on clear days and haze days.