Abstract
East Asia is suffering from severe air pollution problems due to intensive anthropogenic emissions and natural mineral dust aerosols. During transport, the aerosol particles undergo complex mixing processes, resulting in great impacts on regional air quality, human health and climate. In this study, we conducted a long-term observation using an optical particle counter equipped with a polarization detection module (POPC) at an urban site in Beijing. Mass concentrations of both PM 2.5 and PM 10 estimated from POPC compared well with ground-based measurements. The results revealed that the observed depolarization ratio (δ, termed as the ratio of the intensity of the s-polarized signal to the intensity of the 120° backward scattering signal Ts=.s Cp/U) for aerosol particles in the fine mode was generally much lower in summer than that in spring as a result of predominance of different aerosol types. Mineral dust particles in the coarse mode normally had a large δ value (0:3±0:05) owing to their nonspherical shape; however, particles in the fine mode mostly had water-soluble compositions, which led to an apparent decrease of their δ values in particular high relative humidity (RH) conditions. Because the observation site was subject to the impact of frequent dust events in spring, the δ value of particle at 1 μm was almost twice as high as that (0:07±0:01) in summer. Based on size-resolved δ values, anthropogenic pollutants, mineral dust and polluted mineral dust particles and their contribution to local air quality could be well distinguished. About 26.7% of substandard days (daily averaged PM 2.5 concentration larger than 75 μgm -3 ) in Beijing featured high atmospheric loading of coarse-mode particles in winter and springtime. In particular, during severe pollution episodes in winter, the δ values of coarse-mode particles decreased by 13 %, which implies a high possibility of dust-related heterogeneous processes in pollution formation. During dust events, δ values of particles with optical size (Dp) of 5 μm evidently decreased, with an increase of the PM 2.5 =PM 10 ratio as well as RH, indicating the morphological changes of mineral dust. This study confirmed that high RH tends to promote water absorption processes on the dust surface as well as the coating of soluble compounds, and suggested that remote sensing techniques for aerosols may underestimate the impact of dust particles due to the complex mixing of dust and anthropogenic particles in urban areas, and the interaction between dust particles and pollutants should be considered well by the optical model.
| Original language | English |
|---|---|
| Pages (from-to) | 18203-18217 |
| Number of pages | 15 |
| Journal | Atmospheric Chemistry and Physics |
| Volume | 18 |
| Issue number | 24 |
| DOIs | |
| Publication status | Published - Dec 21 2018 |
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All Science Journal Classification (ASJC) codes
- Atmospheric Science
Cite this
Variability of depolarization of aerosol particles in the megacity of Beijing : Implications for the interaction between anthropogenic pollutants and mineral dust particles. / Tian, Yu; Pan, Xiaole; Nishizawa, Tomoaki; Kobayashi, Hiroshi; Uno, Itsushi; Wang, Xiquan; Shimizu, Atsushi; Wang, Zifa.
In: Atmospheric Chemistry and Physics, Vol. 18, No. 24, 21.12.2018, p. 18203-18217.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Variability of depolarization of aerosol particles in the megacity of Beijing
T2 - Implications for the interaction between anthropogenic pollutants and mineral dust particles
AU - Tian, Yu
AU - Pan, Xiaole
AU - Nishizawa, Tomoaki
AU - Kobayashi, Hiroshi
AU - Uno, Itsushi
AU - Wang, Xiquan
AU - Shimizu, Atsushi
AU - Wang, Zifa
PY - 2018/12/21
Y1 - 2018/12/21
N2 - East Asia is suffering from severe air pollution problems due to intensive anthropogenic emissions and natural mineral dust aerosols. During transport, the aerosol particles undergo complex mixing processes, resulting in great impacts on regional air quality, human health and climate. In this study, we conducted a long-term observation using an optical particle counter equipped with a polarization detection module (POPC) at an urban site in Beijing. Mass concentrations of both PM 2.5 and PM 10 estimated from POPC compared well with ground-based measurements. The results revealed that the observed depolarization ratio (δ, termed as the ratio of the intensity of the s-polarized signal to the intensity of the 120° backward scattering signal Ts=.s Cp/U) for aerosol particles in the fine mode was generally much lower in summer than that in spring as a result of predominance of different aerosol types. Mineral dust particles in the coarse mode normally had a large δ value (0:3±0:05) owing to their nonspherical shape; however, particles in the fine mode mostly had water-soluble compositions, which led to an apparent decrease of their δ values in particular high relative humidity (RH) conditions. Because the observation site was subject to the impact of frequent dust events in spring, the δ value of particle at 1 μm was almost twice as high as that (0:07±0:01) in summer. Based on size-resolved δ values, anthropogenic pollutants, mineral dust and polluted mineral dust particles and their contribution to local air quality could be well distinguished. About 26.7% of substandard days (daily averaged PM 2.5 concentration larger than 75 μgm -3 ) in Beijing featured high atmospheric loading of coarse-mode particles in winter and springtime. In particular, during severe pollution episodes in winter, the δ values of coarse-mode particles decreased by 13 %, which implies a high possibility of dust-related heterogeneous processes in pollution formation. During dust events, δ values of particles with optical size (Dp) of 5 μm evidently decreased, with an increase of the PM 2.5 =PM 10 ratio as well as RH, indicating the morphological changes of mineral dust. This study confirmed that high RH tends to promote water absorption processes on the dust surface as well as the coating of soluble compounds, and suggested that remote sensing techniques for aerosols may underestimate the impact of dust particles due to the complex mixing of dust and anthropogenic particles in urban areas, and the interaction between dust particles and pollutants should be considered well by the optical model.
AB - East Asia is suffering from severe air pollution problems due to intensive anthropogenic emissions and natural mineral dust aerosols. During transport, the aerosol particles undergo complex mixing processes, resulting in great impacts on regional air quality, human health and climate. In this study, we conducted a long-term observation using an optical particle counter equipped with a polarization detection module (POPC) at an urban site in Beijing. Mass concentrations of both PM 2.5 and PM 10 estimated from POPC compared well with ground-based measurements. The results revealed that the observed depolarization ratio (δ, termed as the ratio of the intensity of the s-polarized signal to the intensity of the 120° backward scattering signal Ts=.s Cp/U) for aerosol particles in the fine mode was generally much lower in summer than that in spring as a result of predominance of different aerosol types. Mineral dust particles in the coarse mode normally had a large δ value (0:3±0:05) owing to their nonspherical shape; however, particles in the fine mode mostly had water-soluble compositions, which led to an apparent decrease of their δ values in particular high relative humidity (RH) conditions. Because the observation site was subject to the impact of frequent dust events in spring, the δ value of particle at 1 μm was almost twice as high as that (0:07±0:01) in summer. Based on size-resolved δ values, anthropogenic pollutants, mineral dust and polluted mineral dust particles and their contribution to local air quality could be well distinguished. About 26.7% of substandard days (daily averaged PM 2.5 concentration larger than 75 μgm -3 ) in Beijing featured high atmospheric loading of coarse-mode particles in winter and springtime. In particular, during severe pollution episodes in winter, the δ values of coarse-mode particles decreased by 13 %, which implies a high possibility of dust-related heterogeneous processes in pollution formation. During dust events, δ values of particles with optical size (Dp) of 5 μm evidently decreased, with an increase of the PM 2.5 =PM 10 ratio as well as RH, indicating the morphological changes of mineral dust. This study confirmed that high RH tends to promote water absorption processes on the dust surface as well as the coating of soluble compounds, and suggested that remote sensing techniques for aerosols may underestimate the impact of dust particles due to the complex mixing of dust and anthropogenic particles in urban areas, and the interaction between dust particles and pollutants should be considered well by the optical model.
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UR - http://www.scopus.com/inward/citedby.url?scp=85059471561&partnerID=8YFLogxK
U2 - 10.5194/acp-18-18203-2018
DO - 10.5194/acp-18-18203-2018
M3 - Article
AN - SCOPUS:85059471561
VL - 18
SP - 18203
EP - 18217
JO - Atmospheric Chemistry and Physics
JF - Atmospheric Chemistry and Physics
SN - 1680-7316
IS - 24
ER -