Insights into characteristics, sources, and evolution of submicron aerosols during harvest seasons in the Yangtze River delta region, China

摘要

Atmospheric submicron particulate matter (PM) is one of the mostsignificant pollution components in China. Despite its current popularity inthe studies of aerosol chemistry, the characteristics, sources and evolutionof atmospheric PM species are still poorly understood in China,particularly for the two harvest seasons, namely, the summer wheat harvestand autumn rice harvest. An Aerodyne Aerosol Chemical Speciation Monitor(ACSM) was deployed for online monitoring of PM components duringsummer and autumn harvest seasons in urban Nanjing, in the Yangtze Riverdelta (YRD) region of China. PM components were shown to be dominatedby organic aerosol (OA, 39 and 41%) and nitrate (23 and 20%)during the harvest seasons (the summer and autumn harvest). Positive matrixfactorization (PMF) analysis of the ACSM OA mass spectra resolved four OAfactors: hydrocarbon-like mixed with cooking-related OA (HOA + COA), freshbiomass-burning OA (BBOA), oxidized biomass-burning-influenced OA (OOA-BB),and highly oxidized OA (OOA); in particular the oxidized BBOA contributes~80% of the total BBOA loadings. Both fresh and oxidizedBBOA exhibited apparent diurnal cycles with peak concentration at night,when the high ambient relative humidity and low temperature facilitated thepartitioning of semi-volatile organic species into the particle phase. Thefresh BBOA concentrations for the harvests are estimated as BBOA = 15.1 × ( 60–0.26% × OA),where (mass-to-charge ratio) 60 is a marker forlevoglucosan-like species. The (BBOA + OOA-BB)/ΔCO, (ΔCOis the CO minus background CO), decreases as a function of (fraction of 44 in OA signal), which might indicate that BBOA was oxidizedto less volatile OOA, e.g., more aged and low volatility OOA (LV-OOA) duringthe aging process. Analysis of air mass back trajectories indicates that thehigh BB pollutant concentrations are linked to the air masses from thewestern (summer harvest) and southern (autumn harvest) areas.