Gas-to-Aerosol Phase Partitioning of Atmospheric Water-Soluble Organic Compounds at a Rural Site in China: An Enhancing Effect of NH₃ on SOA Formation

Abstract

Partitioning gaseous water-soluble organic compounds (WSOC) to the aerosol phase is a major formation pathway of atmospheric secondary organic aerosols (SOA). However, the fundamental mechanism of the WSOC-partitioning process remains elusive. By simultaneous measurements of both gas-phase WSOC (WSOCg) and aerosol-phase WSOC (WSOCp) and formic and acetic acids at a rural site in the Yangtze River Delta (YRD) region of China during winter 2019, we showed that WSOCg during the campaign dominantly partitioned to the organic phase in the dry period (relative humidity (RH) < 80%) but to aerosol liquid water (ALW) in the humid period (RH > 80%), suggesting two distinct SOA formation processes in the region. In the dry period, temperature was the driving factor for the uptake of WSOCg. In contrast, in the humid period, the factors controlling WSOCg absorption were ALW content and pH, both of which were significantly elevated by NH3 through the formation of NH4NO3 and neutralization with organic acids. Additionally, we found that the relative abundances of WSOCp and NH4NO3 showed a strong linear correlation throughout China with a spatial distribution consistent with that of NH3, further indicating a key role of NH3 in WSOCp formation at a national scale. Since WSOCp constitutes the major part of SOA, such a promoting effect of NH3 on SOA production by elevating ALW formation and WSOCg partitioning suggests that emission control of NH3 is necessary for mitigating haze pollution, especially SOA, in China.

High-resolution observation of stable carbon isotope ratios of water-soluble organic carbon in particle/gas phases at an urban site in China: Using an improved isotope ratio mass spectrometry method

“…It was also found that difference of precursors may lead to the change of WSOC in the gas-particle distribution relationship. The variation of WSOCp in Atlanta was controlled by the aerosol liquid water content (ALWC) under the influence of humidity, which was similar to WSOCp in Chongming island, China (Lv, et al, 2022). While variation of WSOCp in Los Angeles was independent of ALWC, but depended on OC concentration .…”

“…Increase of NH3 leaded to dilution of δ 13 C-WSOCp, enrichment of δ 13 C-WSOCg and increase of WSOCg on an extremely significant level (p<0.01). For there was research found increase of ALWC along with decrease of pH of aerosol in environment of high concentration of NH3 (Shaojun, et al, 2022), which may be conducive to aerosol release WSOCg. Dilution of WSOCp may came from mutual conversion of WSOCp and WSOCg, while enrichment of δ 13 C-WSOCg may came from aging of WSOCg which was generated in an environment of high concentration of NH3 considering increasing concentration of WSOCg.…”

Measurement report: Large contribution of biomass burning and aqueous-phase processes to the wintertime secondary organic aerosol formation in Xi'an, Northwest China

“…The key data sets are archived at the East Asian Paleoenvironmental Science Database, National Earth System Science Data Center, National Science and Technology Infrastructure of China: https://doi.org/10.12262/IEECAS.EAPSD2022004 (Duan et al, 2022). For further information, please contact the corresponding author (rujin.huang@ieecas.cn).…”

“…Numerous studies have elucidated the increasing importance of secondary aerosol in haze pollution (Sun et al, 2016;Huang et al, 2014Huang et al, , 2019An et al, 2019;Duan et al, 2021). However, the formation and evolution of secondary aerosol, especially secondary organic aerosol (SOA), is still not well understood, and this is becoming a critical concern for air pollution research (Gilardoni et al, 2016;Xu et al, 2017;Kuang et al, 2020;Zhang et al, 2021a;Li et al, 2022a;Lv et al, 2022). Deficits in the understanding of variable precursors, complex transformation, and the aging chemistry of SOA lead to insufficient knowledge of its formation as well as uncertainty in model simulations (Shrivastava et al, 2017).…”

Measurement report: Effects of anthropogenic emissions and environmental factors on the formation of biogenic secondary organic aerosol (BSOA) in a coastal city of southeastern China

“…SO 2 also plays an important role in changing SOA formation from BVOC photooxidation and ozonolysis through sulfuric acid formation and acid-catalyzed heterogeneous reactions (Zhao et al, 2018;Xu et al, 2021). In addition, NH 3 and amines can affect the SOA yields and composition through both gas-phase and heterogeneous reactions by reacting with sulfuric or nitric acid to generate secondary inorganic aerosols (SIA) (Ma et al, 2018;Liu et al, 2021;Lv et al, 2022). However, due to complex precursors and atmospheric processes, the combined effects of anthropogenic emissions and meteorological factors on the formation of SOA are not fully understood.…”