Highly time-resolved urban aerosol characteristics during springtime in Yangtze River Delta, China: insights from soot particle aerosol mass spectrometry

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.

Characteristics and Formation Mechanisms of Fine Particulate Nitrate in Typical Urban Areas in China

“…In Nanjing, nitrate varied relatively less during winter than it did during summer, overall, both seasons presented a similar trend-peaking in early morning and reaching minimum in the afternoon. In fact, this pattern was also observed by prior studies conducted during spring [24], autumn [37], and winter in urban Nanjing [38], suggesting that this behavior is similar throughout the year in Nanjing. For Beijing, summer nitrate concentrations responded similarly to the trends observed in the summer in Nanjing, while during winter, Beijing's nitrate concentrations displayed an opposite trend-peaking in the late afternoon/early evening (~7-8 p.m.) and dropping to minimum values in the early morning.…”

“…The sampling locations, sampling periods, and the versions of Aerodyne AMS used for these field campaigns are shown in Figure 1. For Nanjing, a soot-particle AMS (SP-AMS) [23,24] was deployed in urban Nanjing (Jiangxin Island) from 11 August to 18 September 2014, and in the campus of Nanjing University of Information Science and Technology (NUIST) from 20 February to 23 March 2015 (details in [25]). For Beijing, an Aerosol Chemical Speciation Monitor [26] (ACSM, a simplified version of Aerodyne AMS) was deployed during summer (26 June-28 August 2011) and winter (21 November 2011-20 January 2012, both at the Institute of Atmospheric Physics (IAP) of Chinese Academy of Sciences (CAS).…”

Chemical characterization of long-range transport biomass burning emissions to the Himalayas: insights from high-resolution aerosol mass spectrometry

“…6c) also showed significantly high contribution (∼ 25 %) at m/z 44 signal (one of the most reliable marker of oxygenated OA) compared with other ion fragments, e.g., 5 % at m/z 43 (indicator for less oxidized compounds), 1.7 % at m/z 55 (important COA fragment), and 0.4 % at m/z 57 (tracer for traffic-related emission) (Alfarra et al, 2004;Zhang et al, 2005a). The average O / C ratio was 1.07 during this study, which was much higher than those observed at various urban and rural sites in China using the I-A method, e.g., 0.37 in Beijing (Sun et al, 2016), 0.36 in Lanzhou , 0.35 in Nanjing (Wang et al, 2016a), and 0.65 in Ziyang . Moreover, the average O / C ratio was even higher than that of 0.98 from the background site of Mt.…”

“…2 ) at QOMS were quite a bit higher than those obtained at other urban or rural sites in China, whereas carbon and C x H + y ions had relative lower contributions, e.g., 38 % of C x H y O + z and 21 % of oxygen vs. 56 % of C x H + y and 70 % of carbon in urban Lanzhou (Xu et al, 2014), and 37.4 % of C x H y O + z vs. 51.2 % of C x H + y in urban Nanjing (Wang et al, 2016a), suggesting that OA at QOMS were highly aged. Correspondingly, the average highresolution OA mass spectrum (Fig.…”

Formation and characteristics of secondary aerosols in an industrialized environment during cold seasons

“…Our 246 results clearly reveal that this "thermodynamically-driven" mechanism (Ge et that a significant portion of nitrate is due to gas-to-particle conversion rather than processes. Moreover, the aqueous-phase sulfate production is actually insignificant 292 during springtime in urban Nanjing when the temperature is warmer and the air is 293 drier, as revealed in our previous study (Wang et al, 2016b). Therefore, the findings (Fig.…”