Journal article
Characteristics of Daytime-And-Nighttime AOD Differences Over China: A Perspective From CALIOP Satellite Observations and GEOS-Chem Model Simulations
Journal of geophysical research. Atmospheres, Vol.129(8), e2023JD039158
04/28/2024
DOI: 10.1029/2023JD039158
Abstract
We use the GEOS-Chem chemistry transport model to quantify the factors in the diel discrepancy of Aerosol Optical Depth (AOD) retrieved from Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite observations over eastern China. The GEOS-Chem simulation reveals that the AOD below 1 km is 58.5% larger at night than during the daytime, which is comparable to the counterpart of 41.3% from CALIOP (v4.2). Model sensitivity simulations show that the diurnal variation in wind barely impacts the AOD difference between daytime and nighttime, and the increase in AOD at nighttime is primarily caused by the lower temperature at nighttime compared to daytime. Further simulations demonstrate that the low temperature at night increases AOD primarily by increasing relative humidity, and hence particle hygroscopic growth, while the effect of temperature on chemical rate barely influences AOD. CALIOP also observes that the absolute difference in AOD above 1 km between nighttime and daytime is 0.105, while the counterpart in GEOS-Chem simulations is -0.031. This contrast can be partly explained by the factor that the percentage of valid CALIOP retrievals below 5 km is 15%-20% greater at nighttime than in the daytime due to the CALIOP detection limit. Removing the detection limit impact decreases the difference in the CALIOP AOD above 1 km between nighttime and daytime to 0.073.
Aerosols are small particulates suspended in the atmosphere, having adverse impacts on human health, and modifying climate forcing. Satellite-based Aerosol Optical Depth (AOD), while often used as an observation-based indicator of air pollution at global and regional scale, contains not only information on aerosol dry mass concentrations but also information on aerosol optical properties that link mass to optical extinction. We found that satellite-based AOD at night is larger than that in the daytime over eastern China. The disparities cannot be explained by the difference in aerosol dry mass loading alone, and indeed, is primarily caused by larger relative humidity that in turn makes aerosol particle size larger and changes aerosol extinction efficiency via greater hygroscopic growth at night. As the space-borne lidar (CLAIOP) that is designed to measure both daytime and nighttime AOD was decommissioned in August 2023, this study not only reveals the diurnal variation in the relationship between AOD and aerosol dry mass concentrations but also underscores the emergent need and critical importance of nighttime AOD measurements from space for studying air quality and aerosol processes at regional to global scale.
CALIOP observes that Aerosol Optical Depth (AOD) is larger in the nighttime than during the daytime over eastern China Larger nighttime AOD is mainly due to greater hygroscopic growth related to larger relative humidity at night in lower troposphere The CALIOP detection limit difference between daytime and nighttime partly contributes to the larger nighttime AOD below 5 km
Details
- Title: Subtitle
- Characteristics of Daytime-And-Nighttime AOD Differences Over China: A Perspective From CALIOP Satellite Observations and GEOS-Chem Model Simulations
- Creators
- Xiaodong Jiang - China University of GeosciencesYi Wang - China University of GeosciencesLunche Wang - China University of GeosciencesMinghui Tao - China University of GeosciencesJun Wang - University of IowaMeng Zhou - University of IowaXuehui Bai - China University of GeosciencesLu Gui - China University of Geosciences
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Atmospheres, Vol.129(8), e2023JD039158
- Publisher
- Amer Geophysical Union
- DOI
- 10.1029/2023JD039158
- ISSN
- 2169-897X
- eISSN
- 2169-8996
- Number of pages
- 15
- Grant note
- National Natural Science Foundation of China; National Natural Science Foundation of China (NSFC) University of Iowa
- Language
- English
- Date published
- 04/28/2024
- Academic Unit
- Physics and Astronomy; Electrical and Computer Engineering; Chemical and Biochemical Engineering; Iowa Technology Institute; Civil and Environmental Engineering
- Record Identifier
- 9984618502302771
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