Secondary aerosol formation alters CCN activity in the North China Plain

Abstract

Abstract. The formation of secondary aerosols (SA, including secondary organic and inorganic aerosols, SOA and SIA) is the dominant source of aerosol particles in the North China Plain and has a significant impact on the variations of particle size distribution (PNSD) and hygroscopicity. Previous studies have shown that the mechanism of SA formation can be affected by relative humidity (RH), and thus has different influences on the aerosol hygroscopicity and PNSD under different RH conditions. Based on the measurements of size-resolved particle activation ratio (SPAR), hygroscopicity distribution (GF-PDF), PM2.5 chemical composition, PNSD, meteorology and gaseous pollutants in a recent field campaign McFAN (Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain) conducted at Gucheng site from 16th November to 16th December in 2018, the influences of SA formation on CCN activity and CCN number concentration (NCCN) calculation under different RH conditions were studied. Measurements showed that during daytime the SA formation can lead to a significant increase of NCCN and a strong diurnal variation of CCN activity. During periods with minimum RH higher than 50 % in daytime (high RH conditions), SA formation significantly contributed to the particle mass/size changes in wide particle size range of 150 nm to 1000 nm, and lead to the increase of NCCN in particle size range of 200 nm to 300 nm while increase of particle mass concentration mainly in particle size larger than 300 nm. During periods with minimum RH lower than 30 % in daytime (low RH conditions), SA formation mainly contributed to the particle mass/size changes in particle size smaller than 300 nm and so did the increases of both NCCN and particle mass concentration. As a result, upon the same amount of mass increase through SA formation, the increase of NCCN is weaker under high RH conditions while stronger under low RH conditions. Moreover, the diurnal variations of aerosol mixing state (inferred from CCN measurements) due to SA formation was different under different RH conditions, which contributed one of the largest uncertainties in NCCN predictions. By applying aerosol mixing state estimated by number fraction of hygroscopic particles from measurements of particle hygroscopicity or mass fraction of SA from measurements of particle chemical compositions, the NCCN prediction was largely improved with relative deviations smaller than 30 %. This study highlights the impact of SA formation on CCN activity and NCCN calculation, which is of great significance for improving parameterization of SA formation in chemical-transport models and CCN predictions in climate models.

Current Challenges in Visibility Improvement in Sichuan Basin

“…This phenomenon agrees with the study of Jiangchuan Tao et al. (2021), where the secondary aerosol formation contributed to the particle in a broad size range of 150–1,000 nm under high RH conditions in the SB, leading to almost the same mean aerosol diameter under different PM 2.5 levels. However, secondary aerosol formation mainly contributed to the particles smaller than 300 nm under low RH conditions in the NCP, which lead to the increment in the median diameter of aerosol PNSD.…”

Kinetic Limitations Affect Cloud Condensation Nuclei Activity Measurements Under Low Supersaturation

“…(2016) and Tao et al. (2021). The SSs of CCNC were calibrated with monodisperse ammonium sulfate particles (Rose et al., 2008) both before and after the campaign and details about the calibration can be found in Section S1 in Supporting Information .…”

Hygroscopicity of Water‐Soluble PM2.5 in Rural Northwest China: Contrasting Contributors Between Summer and Winter

“…During the high RH, aqueous‐phase secondary aerosol formation was promoted, leading to persistent increases in the number of cloud condensation nuclei, mass concentration of non‐refractory particulate matter of PM 2.5 and especially mass concentration of PM 2.5 secondary aerosol. During the low RH, the secondary aerosol formation dominantly occurred in the gas phase, that generated much less secondary aerosol than aqueous‐phase formation (Kuang et al., 2020; Tao et al., 2021). Aqueous phase processes start with water‐soluble, polar precursors and form SOA that is, more oxygenated than gas SOA as they lead to functionalization or accretion (e.g., acid formation, oligomerization) rather than to breakage of the carbon structure as in gas phase reactions (Ervens et al., 2011).…”