Abstract
Abstract. In this work, the Aerodyne soot particle – aerosol mass spectrometer (SP-AMS) was deployed for the first time during the spring of 2015 in urban Nanjing, a megacity in the Yangtze River Delta (YRD) of China, for online characterization of the submicron aerosols (PM1). The SP-AMS enables real-time and fast quantification of refractory black carbon (rBC) simultaneously with other non-refractory species (ammonium, sulfate, nitrate, chloride, and organics). The average PM1 concentration was found to be 28.2 µg m−3, with organics (45 %) as the most abundant component, following by sulfate (19.3 %), nitrate (13.6 %), ammonium (11.1 %), rBC (9.7 %), and chloride (1.3 %). These PM1 species together can reconstruct ∼ 44 % of the light extinction during this campaign based on the IMPROVE method. Chemically resolved mass-based size distributions revealed that small particles especially ultrafine ones (< 100 nm vacuum aerodynamic diameter) were dominated by organics and rBC, while large particles had significant contributions from secondary inorganic species. Source apportionment of organic aerosols (OA) yielded four OA subcomponents, including hydrocarbon-like OA (HOA), cooking-related OA (COA), semi-volatile oxygenated OA (SV-OOA), and low-volatility oxygenated OA (LV-OOA). Overall, secondary organic aerosol (SOA, equal to the sum of SV-OOA and LV-OOA) dominated the total OA mass (55.5 %), but primary organic aerosol (POA, equal to the sum of HOA and COA) can outweigh SOA in the early morning and evening due to enhanced human activities. High OA concentrations were often associated with high mass fractions of POA and rBC, indicating the important role of anthropogenic emissions during heavy pollution events. The diurnal cycles of nitrate, chloride, and SV-OOA both showed good anti-correlations with air temperatures, suggesting their variations were likely driven by thermodynamic equilibria and gas-to-particle partitioning. On the other hand, in contrast to other species, sulfate, and LV-OOA concentrations increased in the afternoon, and showed no positive correlations with relative humidity (RH), likely indicating the contribution from photochemical oxidation is dominant over that of aqueous-phase processing for their formations. The bivariate polar plots show that the SV-OOA was formed locally, and the variations of hydrogen-to-carbon (H ∕ C) and oxygen-to-carbon (O ∕ C) ratios in the Van Krevelen space further suggests an evolution pathway of SV-OOA to LV-OOA. Our findings regarding springtime aerosol chemistry in Nanjing may have important implications for the air quality remediation in the densely populated regions.
Highlights
In recent years, high concentrations of fine particulate matter (PM2.5) have been frequently observed (Hu et al, 2015), in accompanying with the visibility impairment and occurrence of haze events across large parts of China
We found that the composition-dependent CE rather than a constant CE = 0.5 has negligible effects on the quantification of aerosol species, as the particles were neutralized (Fig. 3a), the mass fraction of ammonium nitrate were < 40 % in almost all cases, and the sampling line relative humidity (RH) was below 10 %
We present for the first time the real-time measurement results using the soot particle – aerosol mass spectrometer (SP-aerosol mass spectrometer (AMS)) on submicron aerosols in urban Nanjing during springtime (13–29 April 2015)
Summary
High concentrations of fine particulate matter (PM2.5) have been frequently observed (Hu et al, 2015), in accompanying with the visibility impairment and occurrence of haze events across large parts of China. PM2.5 affects human health (e.g., Pope and Dockery, 2006; Cao et al, 2012), regional and global climate directly by absorbing and scattering solar radiation or indirectly by acting as cloud condensation nuclei and ice nuclei (e.g., Ghan and Schwartz, 2007; Pöschl, 2005), and the earth’s ecosystem (Carslaw et al, 2010) These effects are predominantly dependent upon the physical and chemical characteristics of fine particles, such as mass concentration, chemical composition, size distribution, and hygroscopicity, all of which are influenced by the emission sources and transformation and evolution processes in the atmosphere. Subsequent offline analyses may introduce artifacts as some semi-volatile species can evaporate during sampling and storage (Dong et al, 2012)
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