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Published June 2016 | public
Journal Article

Towards a quantitative understanding of total OH reactivity: A review

Abstract

Over the past fifty years, considerable efforts have been devoted to measuring the concentration and chemical speciation of volatile organic compounds (VOCs) in ambient air and emissions. Recently, it has become possible to directly determine the overall effect of atmospheric trace gases on the oxidant hydroxyl radicals (OH), by measuring OH reactivity (OH loss frequency). Quantifying total OH reactivity is one way to characterize the roles of VOCs in formation of ground-level ozone and secondary organic aerosols (SOA). Approaches for measuring total OH reactivity in both emissions and ambient air have been progressing and have been applied in a wide range of studies. Here we evaluate the main techniques used to measure OH reactivity, including two methods directly measuring OH decay and one comparative reactivity method (CRM), and summarize the existing experimental and modeling studies. Total OH reactivity varies significantly on spatial, diurnal, seasonal and vertical bases. Comparison with individually detected OH sinks often reveals a significant missing reactivity, ranging from 20% to over 80% in some environments. Missing reactivity has also been determined in most source emission studies. These source measurements, as well as numerical models, have indicated that both undetected primary emissions and unmeasured secondary products could contribute to missing reactivity. A quantitative understanding of total OH reactivity of various sources and ambient environments will enhance our understanding of the suite of compounds found in emissions as well as chemical processes, and will also provide an opportunity for the improvement of atmospheric chemical mechanisms.

Additional Information

© 2016 Elsevier Ltd. Received 20 November 2015; Received in revised form 3 March 2016; Accepted 4 March 2016; Available online 7 March 2016. This study was funded by the Natural Science Foundation for Outstanding young Scholars (grant no. 41125018) and a Natural Science Foundation key project (grant no. 411330635). The research was also supported by the European Commission Partnership with China on Space Data (PANDA project). Special thanks to Bin Yuan, Jing Zheng from Peking University and Xin Huang from Nanjing University for the help.

Additional details

Created:
August 22, 2023
Modified:
October 18, 2023