TY - JOUR

T1 - Photochemical impacts of haze pollution in an urban environment

AU - Hollaway, Michael

AU - Wild, Oliver

AU - Yang, Ting

AU - Sun, Yele

AU - Xu, Weiqi

AU - Xie, Conghui

AU - Whalley, Lisa

AU - Slater, Eloise

AU - Heard, Dwayne

AU - Liu, Dantong

PY - 2019/8/1

Y1 - 2019/8/1

N2 - Rapid economic growth in China over the past 30 years has resulted in significant increases in the concentrations of small particulates (PM2.5 ) over the city of Beijing. In addition to health problems, high aerosol loading can impact visibility and thus reduce photolysis rates over the city leading to potential implications for photochemistry. Photolysis rates are highly sensitive not only to the vertical distribution of aerosols but also to their composition as this can impact how the incoming solar radiation is scattered or absorbed. This study, for the first time, uses aerosol composition measurements and lidar optical depth to drive the Fast-JX photolysis scheme and quantify the photochemical impacts of different aerosol species during the Air Pollution and Human Health (APHH) measurement campaigns in Beijing in November–December 2016 and May–June 2017. This work demonstrates that severe haze pollution events (PM2.5 > 75 μgm-3 ) occur during both winter and summer leading to reductions in O3 photolysis rates of 27–34 % (greatest in winter) and reductions in NO2 photolysis of 40–66 % (greatest in summer) at the surface. It also shows that in spite of much lower PM2.5 concentrations in the summer months, the absolute changes in photolysis rates are larger for both O3 and NO2 . In the winter absorbing species such as black carbon dominate the photolysis response to aerosols leading to mean reductions in J[O1 D] and J[NO2 ] in the lowest 1 km of 24 % and 23 % respectively. In contrast in the summer, scattering aerosol such as organic matter dominate the response leading to mean decreases of 2–3 % at the surface and increases of 8–10 % at higher altitudes (3–4 km). During these haze events in both campaigns, the influence of aerosol on photolysis rates dominates over that from clouds. These large impacts on photochemistry can have significant implications for concentrations of important atmospheric oxidants such as the hydroxyl radical. Idealised photochemical box model studies show that such large impacts on photochemistry could lead to a 12 % reduction in surface O3 (3 % for OH) due to haze pollution. This highlights that PM2.5 mitigation strategies could have important implications for the oxidation capacity of the atmosphere both at the surface and in the free troposphere.

AB - Rapid economic growth in China over the past 30 years has resulted in significant increases in the concentrations of small particulates (PM2.5 ) over the city of Beijing. In addition to health problems, high aerosol loading can impact visibility and thus reduce photolysis rates over the city leading to potential implications for photochemistry. Photolysis rates are highly sensitive not only to the vertical distribution of aerosols but also to their composition as this can impact how the incoming solar radiation is scattered or absorbed. This study, for the first time, uses aerosol composition measurements and lidar optical depth to drive the Fast-JX photolysis scheme and quantify the photochemical impacts of different aerosol species during the Air Pollution and Human Health (APHH) measurement campaigns in Beijing in November–December 2016 and May–June 2017. This work demonstrates that severe haze pollution events (PM2.5 > 75 μgm-3 ) occur during both winter and summer leading to reductions in O3 photolysis rates of 27–34 % (greatest in winter) and reductions in NO2 photolysis of 40–66 % (greatest in summer) at the surface. It also shows that in spite of much lower PM2.5 concentrations in the summer months, the absolute changes in photolysis rates are larger for both O3 and NO2 . In the winter absorbing species such as black carbon dominate the photolysis response to aerosols leading to mean reductions in J[O1 D] and J[NO2 ] in the lowest 1 km of 24 % and 23 % respectively. In contrast in the summer, scattering aerosol such as organic matter dominate the response leading to mean decreases of 2–3 % at the surface and increases of 8–10 % at higher altitudes (3–4 km). During these haze events in both campaigns, the influence of aerosol on photolysis rates dominates over that from clouds. These large impacts on photochemistry can have significant implications for concentrations of important atmospheric oxidants such as the hydroxyl radical. Idealised photochemical box model studies show that such large impacts on photochemistry could lead to a 12 % reduction in surface O3 (3 % for OH) due to haze pollution. This highlights that PM2.5 mitigation strategies could have important implications for the oxidation capacity of the atmosphere both at the surface and in the free troposphere.

KW - Photolysis

KW - Haze

KW - Air Pollution

KW - Beijing

U2 - 10.5194/acp-19-9699-2019

DO - 10.5194/acp-19-9699-2019

M3 - Journal article

VL - 19

SP - 9699

EP - 9714

JO - Atmospheric Chemistry and Physics

JF - Atmospheric Chemistry and Physics

SN - 1680-7316

IS - 15

ER -