Effect of bromine and iodine chemistry on tropospheric ozone over Asia-Pacific using the CMAQ model

Yeqi Huang; Xingcheng Lu; Jimmy C H Fung; Golam Sarwar; Zhenning Li; Qinyi Li; Alfonso Saiz-Lopez; Alexis K H Lau

doi:10.1016/j.chemosphere.2020.127595

Effect of bromine and iodine chemistry on tropospheric ozone over Asia-Pacific using the CMAQ model

Chemosphere. 2021 Jan:262:127595. doi: 10.1016/j.chemosphere.2020.127595. Epub 2020 Jul 10.

Authors

Yeqi Huang¹, Xingcheng Lu¹, Jimmy C H Fung², Golam Sarwar³, Zhenning Li⁴, Qinyi Li⁵, Alfonso Saiz-Lopez⁵, Alexis K H Lau⁶

Affiliations

¹ Division of Environment and Sustainability, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
² Division of Environment and Sustainability, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China; Division of Mathematics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China. Electronic address: majfung@ust.hk.
³ Center for Environmental Measurement and Modeling, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA.
⁴ Institute of Environment, Energy and Sustainability, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China.
⁵ Department of Atmospheric Chemistry and Climate, Institute of Physical Chemistry Rocasolano, CSIC, Madrid, 28006, Spain.
⁶ Division of Environment and Sustainability, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China; Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China.

Abstract

Recent studies have focused on the chemistry of tropospheric halogen species which are able to deplete tropospheric ozone (O₃). In this study, the effect of bromine and iodine chemistry on tropospheric O₃ within the annual cycle in Asia-Pacific is investigated using the CMAQ model with the newly embedded bromine and iodine chemistry and a blended and customized emission inventory considering marine halogen emission. Results indicate that the vertical profiles of bromine and iodine species show distinct features over land/ocean and daytime/nighttime, related to natural and anthropogenic emission distributions and photochemical reactions. The halogen-mediated O₃ loss has a strong seasonal cycle, and reaches a maximum of -15.9 ppbv (-44.3%) over the ocean and -13.4 ppbv (-38.9%) over continental Asia among the four seasons. Changes in solar radiation, dominant wind direction, and nearshore chlorophyll-a accumulation all contribute to these seasonal differences. Based on the distances to the nearest coastline, the onshore and offshore features of tropospheric O₃ loss caused by bromine and iodine chemistry are studied. Across a coastline-centric 400-km-wide belt from onshore to offshore, averaged maximum gradient of O₃ loss reaches 1.1 ppbv/100 km at surface level, while planetary boundary layer (PBL) column mean of O₃ loss is more moderate, being approximately 0.7 ppbv/100 km. Relative high halogen can be found over Tibetan Plateau (TP) and the largest O₃ loss (approximately 4-5 ppbv) in the PBL can be found between the western boundary of the domain and the TP. Halogens originating from marine sources can potentially affect O₃ concentration transported from the stratosphere over the TP region. As part of efforts to improve our understanding of the effect of bromine and iodine chemistry on tropospheric O₃, we call for more models and monitoring studies on halogen chemistry and be considered further in air pollution prevention and control policy.

Keywords: Bromine and iodine chemistry; CMAQ; Onshore/offshore features; Tropospheric O(3); Vertical structure.

MeSH terms

Air Pollutants / analysis*
Air Pollution / statistics & numerical data*
Asia
Bromine
Halogens / chemistry
Iodides
Iodine / analysis*
Ozone / analysis*
Seasons

Substances

Air Pollutants
Halogens
Iodides
Ozone
Iodine
Bromine

Grants and funding

EPA999999/ImEPA/Intramural EPA/United States