Measurement report: The effect of aerosol chemical composition on light scattering due to the hygroscopic swelling effect

Abstract

Abstract. Liquid water in aerosol particles has a significant effect on their optical properties, especially on light scattering, whose dependence on chemical composition is investigated here using measurements made in southern Beijing in 2019. The effect is measured by the particle light scattering enhancement f(RH), where RH denotes the relative humidity, which is found to be positively and negatively impacted by the proportions of inorganic and organic matter, respectively. Black carbon is also negatively correlated. The positive impact is more robust when the inorganic matter mass fraction was smaller than 40 % (R=0.93, R: the Pearson's correlation coefficient), becoming weaker as the inorganic matter mass fraction gets larger (R=0.48). A similar pattern was also found for the negative impact of the organic matter mass fraction. Nitrate played a more significant role in aerosol hygroscopicity than sulfate in Beijing. However, the deliquescence point of ambient aerosols was at about RH = 80 % when the ratio of the sulfate mass concentration to the nitrate mass concentration of the aerosol was high (mostly higher than ∼ 4). Two schemes to parameterize f(RH) were developed to account for the deliquescent and non-deliquescent effects. Using only one f(RH) parameterization scheme to fit all f(RH) processes incurs large errors. A piecewise parameterization scheme is proposed, which can better describe deliquescence and reduces uncertainties in simulating aerosol hygroscopicity.

Differentiating the Contributions of Particle Concentration, Humidity, and Hygroscopicity to Aerosol Light Scattering at Three Sites in China

“…The observation site in BJ is located in the southern suburbs of the city (39.81°N, 116.48°E), surrounded by the fifth Ring Road and industrial parks. Pollutants affecting the area include those from nearby industrial activities, traffic emissions, and transport from the southern part of the North China Plain (Ren et al., 2021; D. Zhang et al., 2022). The observation site in NJ is located in the northern suburban area of the city (32.20°N, 118.72°E), surrounded by several large‐scale industries, for example, electric power, steel, and petrochemical plants.…”

The Impacts of Dust Storms With Different Transport Pathways on Aerosol Chemical Compositions and Optical Hygroscopicity of Fine Particles in the Yangtze River Delta

“…Ren et al. (2021) showed that the environmental aerosol deliquescence phenomenon is easy to occur when the mass ratio of sulfate to nitrate ($${R}_{{\text{SO}}_{4}^{2-}/{\text{NO}}_{3}^{-}}$$) is greater than ∼4. According to our measurement, $${R}_{{\text{SO}}_{4}^{2-}/{\text{NO}}_{3}^{-}}$$ in PM 2.5 during Dust1 and Dust2 are always higher than 4 (Figure S7 in Supporting Information ), which is the reason for environmental aerosol deliquescence during dust periods.…”

“…The DRH of AS-AN particles increased with the decrease of ammonium nitrate content, closing to the DRH of pure ammonium sulfate particles (Sun et al, 2018). Ren et al (2021) showed that the environmental aerosol deliquescence phenomenon is easy to occur when the mass ratio of sulfate to nitrate ( ) is close to 1.9. All the results demonstrate that DS can effectively reduce aerosol optical hygroscopicity by increasing the hydrophobic aerosols (such as mineral aerosols) although they may promote the formation of secondary aerosols (Shi et al, 2008).…”

Vertical profiles of cloud condensation nuclei number concentration and its empirical estimate from aerosol optical properties over the North China Plain

“…The integrating nephelometer (model 3565, TSI Inc.) can continuously measure aerosol scattering coefficients (σ ) at three wavelengths (450, 550, and 700 nm) with a time resolution of 1 s. Previous studies have shown that σ becomes larger with increasing relative humidity (RH) due to aerosol hygroscopic growth (e.g., L. Zhang et al, 2015;Ren et al, 2021). Hence, the scattering values were adjusted using a correction factor (Anderson and Ogren, 1998).…”