Different effects of anthropogenic emissions and aging processes on the mixing state of soot particles in the nucleation and accumulation modes

Abstract

Abstract. In this study, the mixing state of size-resolved soot particles and their influencing factors were investigated based on a 5-month aerosol volatility measurement at a suburban site (Xingtai, XT) in the central North China Plain (NCP). The volatility and mixing state of soot-containing particles at XT were complex, caused by multiple pollution sources and various aging processes. The results suggest that anthropogenic emissions can weaken the mean volatility of soot-containing particles and enhance their degree of external mixing. There were fewer externally mixed soot particles in warm months (June, July, and August) than in cold months (May, September, and October). Monthly variations in the mean coating depth (Dc,mean) of volatile matter on soot particles showed that the coating effect was stronger in warm months than in cold months, even though aerosol pollution was heavier in cold months. Moreover, the volatility was stronger, and the degree of internal mixing was higher in nucleation-mode soot-containing particles than in accumulation-mode soot-containing particles. Relationships between Dc,mean and possible influencing factors (temperature (T), relative humidity (RH), and particulate matter, with diameters ranging from 10 to 400 nm) further suggest that high ambient T and RH in a polluted environment could promote the coating growth of accumulation-mode soot particles. However, high ambient T but low RH in a clean environment was beneficial to the coating growth of nucleation-mode soot particles. Our results highlight the diverse impact of anthropogenic emissions and aging processes on the mixing state of soot particles in different modes, which should be considered separately in models to improve the simulation accuracy of aerosol absorption.

Markedly different impacts of primary emissions and secondary aerosol formations on aerosol mixing states revealed by simultaneous measurements of CCNC, V/HTDMA and SP2

“…The NFH was consistently lower than NFV and NFnoBC (the average difference between NFH and NFnoBC was about 0.2), especially during the moderately polluted period, suggesting a significant fraction of volatile BC-free aerosols had hygroscopicity lower than 0.07 but were still CCN-active and therefore not fully hydrophobic. different aerosol mode (Aitken mode) to particles larger than 100nm (Wang et al, 2022). For particle sizes larger than 100 nm, there were peaks in the afternoon for MAF, NFH, NFV and NFnoBC, due to the increase in secondary aerosol compositions like nitrate and SOA, and the decrease of POA and BC.…”

“…Using simple internally mixing state assumptions for aerosol chemical compositions in estimating CCN number concentrations can lead to substantial overestimations (Deng et al, 2013;Farmer et al, 2015;Ren et al, 2018;Ching et al, 2017Ching et al, , 2019Tao et al, 2021). The aerosol mixing state varies widely due to complex emissions and atmospheric transformations, leading to significant uncertainties in estimating the effects of aerosol based on simplified mixing state assumptions (Ervens, 2015;Wang et al, 2022;Fu et al, 2022).…”

“…Although both SP2 and VTDMA techniques depend on the evaporation of non-refractory compositions, only the rBC remains in SP2 measurements, whereas the non-refractory composition evaporations depend on thermodenuder temperature in VTDMA measurements. Thus, measurements of an SP2 are highly correlated to those of a VTDMA at high temperatures, with their differences reflecting variations in aerosol density, shape or volatility (Philippin et al, 2004;Wehner et al, 2009;Adachi et al, 2018Wang et al, 2022). HTDMA and VTDMA can be applied in combination to study the influence of aerosol mixing state on its hygroscopicity and volatility (Zhang et al, 2016;Cai et al, 2017;.…”

“…The mixing state of primary aerosols can vary greatly depending on their type and emission conditions (Cheng et al 2012;Wang et al, 2022;Ting et al, 2018;Liu et al, 2021), and can be significantly altered during aging processes or secondary formations (Wehner et al 2009;Cheng et al 2012;Wang et al, 2022;Tomlin et al, 2021;Lata et al, 2021). Primary aerosol emissions such as biomass burning, fossil fuel combustion and cooking tend to contribute to weakly hygroscopic (Herich et al, 2008(Herich et al, , 2009Wang et al, 2020;Kim et al, 2020) and low-volatility aerosols (Hong et al, 2017;Saha et al, 2018), while formation of secondary aerosol including aging of BC-containing aerosols and primary organic aerosols mainly contribute to aerosols with strong CCN activity (Mei et al, 2013;Ma et al, 2016;Tao et al, 2021) and high hygroscopicity (Chen et al, 2018;Kim et al, 2020;Wang et al, 2020).…”