Abstract
Abstract. The relationship between relative humidity (RH) and extinction properties is of widespread concern. In this study, a hygroscopic parameter (κ) and the volume fraction of elemental carbon (EC) were used to characterize the chemical characteristics of particles, and a core-shell model was built based on these characteristics. The size distribution, chemical composition, and RH were measured in Nanjing from 15 October to 13 November 2013. The model-derived extinction coefficients of particles were fit with the program of coated spheres according to Bohren and Huffman (2008) (BHCOAT), and the modeled values correlated well with the measurement-derived extinction coefficients (r2 = 0. 81), which suggested that the core-shell model produced reasonable results. The results show that more than 81 % of the extinction coefficient in Nanjing was due to particles in the 0.2–1.0 µm size range. Under dry conditions, the higher mass fraction of particles in the 0.2–1.0 µm size range caused the higher extinction coefficient. An increase in RH led to a significant increase in the extinction coefficient, although the increases differed among the different size segments. For λ = 550 nm, the extinction coefficient from the 0.01–0.2, 0.2–0.5, and 1.0–2.0 µm size ranges increased significantly with the increase in RH, whereas the extinction contributions from the 0.5–1.0 and 2.0–10.0 µm size ranges to the extinction coefficient decreased slightly.
Highlights
Degradation of visibility is likely the most readily perceived impact of aerosol pollution, and it has been used as a visual indicator of ambient air quality (Watson, 2002)
Because the aerosol measurements in high relative humidity (RH) are prone to errors, we excluded the data with RH > 90 % and visibility < 1 km
The picture shows that the visibility has a strong negative correlation with PM2.5 and RH (r = −0.7 and −0.62, respectively)
Summary
Degradation of visibility is likely the most readily perceived impact of aerosol pollution, and it has been used as a visual indicator of ambient air quality (Watson, 2002). Visibility throughout the world has generally decreased in recent decades, especially in Asia. In Guangzhou, one of the largest cities in the Pearl River Delta (PRD), low visibility occurs on 150 days per year (Deng et al, 2008). In the Yangtze River Delta (YRD) region, visibility has decreased at a rate of 2.4 km decade−1 (Gao et al, 2011). Visibility degradation is mainly caused by the increase in particle number or mass concentration. Visibility problems have received unprecedented attention in recent years
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