Measurement report: Dust impact on hygroscopicity and volatility of submicron aerosols: Based on the observation in April of Beijing

Abstract. Understanding the aerosol hygroscopicity and volatility is crucial for determining their effects on the environment and climate. As a typical natural aerosol, the dust impact on fine particles' hygroscopicity and volatility remains inadequately understood. Simultaneous measurements of aerosol hygroscopicity and volatility were performed using Volatility-Hygroscopicity Tandem Differential Mobility Analyzer during April 2024 in Beijing. During this period, mean hygroscopic growth factor (HGF) of 50, 80, 110, 150, 200, and 300 nm were 1.20±0.07, 1.28±0.07, 1.32±0.07, 1.36±0.08, 1.40±0.09, and 1.43±0.13, respectively. The mean volatile shrink factor (VSF) was 0.48±0.05, 0.52±0.04, 0.53±0.05, 0.53±0.06, 0.53±0.07, and 0.54±0.10. Particles from anthropogenic emissions were dominated by more hygroscopic and volatile components, while particles influenced by natural sources (such as dust) had lower hygroscopicity and volatility. The case study highlighted the impact of dust on hygroscopicity and volatility for accumulated mode particles. Before dust arrival, more hygroscopic and very volatile mode were more prominent, and HGF increased and VSF decreased with diameter. When dust arrived, the number fraction of more hygroscopic mode (NF_MH) dropped to 0.54 (200 nm) and 0.33 (300 nm), while number fraction of very volatile mode (NF_VV) fell to 0.73 (200 nm) and 0.47 (300 nm), respectively. This reflected a shift toward the hydrophobic and non-volatile components. During dust period, the size dependence showed that HGF peaked at 150 nm and declined, whereas VSF rose with diameter. The mean HGF and VSF at 300 nm were 1.20 and 0.74 during dust period, suggesting that particles at 300 nm were hydrophobic and less volatile.