Response of ozone to changes in hydrocarbon and nitrogen oxide concentrations in outdoor smog chambers filled with Los Angeles air |
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| Institution: | 1. Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, UTM Skudai, Johor 81310, Malaysia;2. Faculty of Mechanical Engineering, Universiti Malaysia Pahang, Pekan, Pahang 26600, Malaysia;1. State Key Laboratory for Structural Chemistry of Unstable and Stable Species, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China;4. College of Chemistry, Liaoning University, Shenyang 110036, China;5. State Key Laboratory of Severe Weather & Key Laboratory for Atmospheric Chemistry of CMA, Institute of Atmospheric Composition, Chinese Academy of Meteorological Sciences, Beijing 100081, China;6. State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China;1. College of Environmental Sciences and Engineering, China West Normal University, Nanchong, Sichuan, China;2. College of Architecture & Environment, Sichuan University, Chengdu, China;3. Key Laboratory of Nanchong City of Ecological Environment Protection and Pollution Prevention in Jialing River Basin, China West Normal University, Nanchong, China;4. College of Biology and Environmental Sciences, Jishou University, Jishou, Hunan, China;1. Research Center for Atmospheric Environment, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China;2. Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China;3. College of Resources and Environment, Chongqing School, University of the Chinese Academy of Sciences (UCAS Chongqing), Chongqing 400714, China;4. College of Environmental and Chemical Engineering, Chongqing Three Gorges University, Chongqing 404199, China;5. Key Laboratory for Urban Habitat Environmental Science and Technology, School of Environment and Energy, Peking University Shenzhen Graduate School, Lishui Road, Nanshan District, Shenzhen 518055, China;6. SKL-ESPC and BIC-ESAT, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China;7. College of Architecture & Environment, Sichuan University, Chengdu 610065, China |
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| Abstract: | During the summer portion of the 1987 Southern California Air Quality Study (SCAQS), outdoor smog chamber experiments were performed on Los Angeles air to determine the response of maximum ozone levels, O3(max), to changes in the initial concentrations of hydrocarbons, HC, and nitrogen oxides, NOx. These captive-air experiments were conducted in downtown Los Angeles and in the downwind suburb of Claremont. Typically, eight chambers were filled with LA air in the morning. In some chambers the initial HC and/or NOx concentrations were changed by 25% to 50% by adding various combinations of a mixture of HC, clean air, or NOx. The O3 concentration in each chamber was monitored throughout the day to determine O3(max).An empirical mathematical model for O3(max) was developed from regression fits to the initial HC and NOx concentrations and to the average daily temperature at both sites. This is the first time that a mathematical expression for the O3-precursor relationship and the positive effect of temperature on O3(max) have been quantified using captive-air experiments. An ozone isopleth diagram prepared from the empirical model was qualitatively similar to those prepared from photochemical mechanisms. This constitutes the first solely empirical corroboration of the O3 contour shape for Los Angeles.To comply with the Federal Ozone Standard in LA, O3(max) must be reduced by approximately 50%. Several strategies for reducing O3(max) by 50% were evaluated using the empirical model. For the average initial conditions that we measured in LA, the most efficient strategy is one that reduces HC by 55–75%, depending on the ambient HC/NOx ratio. Any accompanying reduction in NOx would be counter-productive to the benefits of HC reductions. In fact, reducing HC and NOx simultaneously requires larger percentage reductions for both than the reduction required when HC alone is reduced. The HC-reduction strategy is the most efficient on average, but no single strategy is the optimum every day. |
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