Highly time-resolved urban aerosol characteristics during springtime inYangtze River Delta, China: insights from soot particle aerosol massspectrometry

摘要

In this work, the Aerodyne soot particle – aerosol mass spectrometer(SP-AMS) was deployed for the first time during the spring of 2015 in urbanNanjing, a megacity in the Yangtze River Delta (YRD) of China, for onlinecharacterization of the submicron aerosols (PM). The SP-AMS enablesreal-time and fast quantification of refractory black carbon (BC)simultaneously with other non-refractory species (ammonium, sulfate, nitrate,chloride, and organics). The average PM concentration was found to be28.2 µg m, with organics (45 %) as the most abundantcomponent, following by sulfate (19.3 %), nitrate (13.6 %), ammonium(11.1 %), BC (9.7 %), and chloride (1.3 %). These PMspecies together can reconstruct ∼ 44 % of the light extinctionduring this campaign based on the IMPROVE method. Chemically resolvedmass-based size distributions revealed that small particles especiallyultrafine ones ( 100 nm vacuum aerodynamic diameter) weredominated by organics and BC, while large particles had significantcontributions from secondary inorganic species. Source apportionment oforganic aerosols (OA) yielded four OA subcomponents, includinghydrocarbon-like OA (HOA), cooking-related OA (COA), semi-volatile oxygenatedOA (SV-OOA), and low-volatility oxygenated OA (LV-OOA). Overall, secondaryorganic aerosol (SOA, equal to the sum of SV-OOA and LV-OOA) dominated thetotal OA mass (55.5 %), but primary organic aerosol (POA, equal to thesum of HOA and COA) can outweigh SOA in the early morning and evening due toenhanced human activities. High OA concentrations were often associated withhigh mass fractions of POA and BC, indicating the important role ofanthropogenic emissions during heavy pollution events. The diurnal cycles ofnitrate, chloride, and SV-OOA both showed good anti-correlations with airtemperatures, suggesting their variations were likely driven by thermodynamicequilibria and gas-to-particle partitioning. On the other hand, in contrastto other species, sulfate, and LV-OOA concentrations increased in theafternoon, and showed no positive correlations with relative humidity (RH),likely indicating the contribution from photochemical oxidation is dominantover that of aqueous-phase processing for their formations. The bivariatepolar plots show that the SV-OOA was formed locally, and the variations ofhydrogen-to-carbon (H ∕ C) and oxygen-to-carbon (O ∕ C) ratios in theVan Krevelen space further suggests an evolution pathway of SV-OOA to LV-OOA.Our findings regarding springtime aerosol chemistry in Nanjing may haveimportant implications for the air quality remediation in the denselypopulated regions.