Abstract
Fine particulate matters (PM2.5) and relative humidity (RH) in the ambient atmosphere are the leading anthropogenic and natural factors changing atmospheric horizontal visibility. Based on the analysis of environmental and meteorological data observed over 2013–2019 in Nanjing, an urban area in East China, this study investigated the influences of PM2.5 and RH on atmospheric visibility changes over recent years. The visibility had significantly negative correlations with the PM2.5 concentrations and RH changes. The nonlinear relationships existed between PM2.5 concentrations and visibility, as well as between RH and visibility, with the inflection points in the atmospheric visibility changes. The PM2.5 inflection concentrations were 81.0 μg m−3, 76.0 μg m−3, 49.0 μg m−3, and 33.0 μg m−3, respectively, for the RH ranges of RH < 60%, 60% ≤ RH < 80%, 80% ≤ RH < 90%, and RH ≥ 90%, indicating that the improvement of visibility with reducing PM2.5 concentrations could be more difficult under the humid meteorological condition. The visibility changes were most sensitive to PM2.5 concentrations in the RH range of 60–80% in this urban area of East China. The relative contributions of natural factor RH and anthropogenic factor PM2.5 to variations of wintertime atmospheric visibility were quantified with 54.3% and 45.7%, respectively, revealing an important role of natural factor RH in the change of atmospheric visibility in the urban area of East Asian monsoon region.
Highlights
Atmospheric horizontal visibility is meteorologically defined as the distance at which a normal observer can perceive a black object viewed against the horizon [1].For the air environment, visibility can express the ambient atmospheric opacity reflecting the levels of air pollution, especially haze pollution resulting from high aerosol concentrations, which could deteriorate atmospheric visual range [1,2]
The main objectives of this study were to recognize the influences of anthropogenic factor PM2.5 and natural factor relative humidity (RH) on atmospheric visibility change and to quantify the relative contributions of PM2.5 and RH to visibility change over recent years in an urban area of East China
Anthropogenic and natural factors affecting visibility change were investigated based on data of environmental and meteorological observations over 2013–2019 in Nanjing, an urban area of East
Summary
Atmospheric horizontal visibility (hereinafter, visibility) is meteorologically defined as the distance at which a normal observer can perceive a black object viewed against the horizon [1].For the air environment, visibility can express the ambient atmospheric opacity reflecting the levels of air pollution, especially haze pollution resulting from high aerosol concentrations, which could deteriorate atmospheric visual range [1,2]. The changes in atmospheric visibility in long-term data of observation is of major interest in air pollution studies with climatology of atmospheric environment [9,10,11,12]. Visibility is determined by the light extinctions of aerosol particles [13,14] and gaseous pollutants (NOx, SO2 and volatile organic compounds (VOCs)) [5,15,16] in the ambient atmosphere. The gaseous species have much weaker light extinction for less influence on visibility [17]. The size distribution, chemical composition, and mass concentrations of aerosol particles can heavily influence the extinction of aerosols changing atmospheric visibility [18,19,20]
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