Organic aerosol volatility and viscosity in North China Plain: Contrast between summer and winter

Abstract

Abstract. Volatility and viscosity have substantial impacts on gas-particle partitioning, formation and evolution of aerosol, and hence the predictions of aerosol related air quality and climate effects. Here aerosol volatility and viscosity at a rural site (Gucheng) and an urban site (Beijing) in North China Plain (NCP) in summer and winter were investigated by using a thermodenuder coupled with high resolution aerosol mass spectrometer. The effective saturation concentration (C*) of organic aerosol (OA) in summer was smaller than that in winter (0.55 μg m−3 vs. 0.71–0.75 μg m−3), indicating that OA in winter in NCP is more volatile due to enhanced primary emissions from coal combustion and biomass burning. The volatility distributions varied largely different among different OA factors. In particular, we found that hydrocarbon-like OA (HOA) contained more non-volatile compounds compared to coal combustion related OA. The more oxidized oxygenated OA (MO-OOA) showed overall lower volatility than less oxidized OOA (LO-OOA) in both summer and winter, yet the volatility of MO-OOA was found to be relative humidity (RH) dependent showing more volatile properties at higher RH. Our results demonstrated the different composition and chemical formation pathways of MO-OOA under different RH levels. The glass transition temperature (Tg) and viscosity of OA in summer and winter are estimated using the recently developed parameterization formula. Our results showed that the Tg of OA in summer in Beijing (291.5 K) was higher than that in winter (289.7–290.0 K), while it varied greatly among different OA factors. The viscosity suggested that OA existed mainly as solid in winter in Beijing, but as semi-solids in Beijing in summer and Gucheng in winter. These results have important implications that kinetically limited gas-particle partitioning may need to be considered when simulating secondary OA formation in NCP.

Volatility parameterization of ambient organic aerosols at a rural site of the North China Plain

“…Moreover, the fraction of organic species and inorganic salts of nonrefractory submicron aerosol species (NR-PM1) in Beijing in winter 2018 were about 48 % and 52 %, respectively (Zhou et al, 2020). The fraction of organic species and inorganic salts in total particulate matters (PM) in a rural site (Gucheng in Hebei province) in winter 2018 were about 40 % and 60 %, respectively (Xu et al, 2021). The mass ratios of the inorganic salt to organic species were close to 1 : 1, which was similar to that of our laboratory tests (i.e., no.…”

Primary Emissions and Secondary Aerosol Processing During Wintertime in Rural Area of North China Plain

“…The setup and operations of AMS were the same as previous studies (Xu et al., 2021). Briefly, ambient particles with size larger than 2.5 μm were removed first by a PM 2.5 cyclone (model URG‐2000‐30ED), and the rest particles were dried by a Nafion dryer.…”

Size-resolved characterization of organic aerosol in the North China Plain: new insights from high resolution spectral analysis

“…However, f 55 /f 57 was much lower at the rural site (1.3 -1.5) due to the negligible influence of cooking emissions. 29 Figure 3 shows the diurnal evolution of size-resolved O/C ratios and oxidation state during three campaigns. The O/C ratios and oxidation state of OA showed overall increasing trends across all sizes in the afternoon in both summer and winter, indicating the formation of oxidized SOA through photochemical processing.…”

“…PMF analysis was also performed to OA of all sizes assuming constant factor profiles across different sizes. In addition, PMF analysis of high-resolution mass spectra of bulk OA were performed, and the results are reported in Xu et al29 FiguresS2 and S3show the comparisons of OA composition between size-resolved PMF, size-all PMF, and bulk OA PMF. The fractions of SOA from size-resolved PMF were lower than that from size-all PMF in winter in both Beijing (30.6% vs. 39.9%) and Gucheng (44.8% vs. 54.9%), while they were comparable in Beijing in summer (78.5% vs. 79.2%).…”