Spatial and temporal variations in San Joaquin Valley fog chemistry |
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| Institution: | 1. Université Clermont Auvergne, CNRS, UMR 6016, Laboratoire de Météorologie Physique, F-63000 Clermont-Ferrand, France;2. Université Lille, CNRS, UMR 8518 - LOA - Laboratoire d''Optique Atmosphérique, F-59000 Lille, France;3. Université Clermont Auvergne, Institut Universitaire de Technologie d''Allier, Montluçon, France;1. State Key Joint Laboratory of Environmental Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China;2. State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex, Beijing 100084, China;3. Zachry Department of Civil Engineering, Texas A&M University, College Station, TX, United States;4. School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, United States;5. State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, China;6. Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, 999077, Hong Kong, China;7. SKL-ESPC and BIC-ESAT, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China;1. State Environmental Protection Key Laboratory of Urban Ambient Air Particulate Matter Pollution Prevention and Control, Center for Urban Transport Emission Research, College of Environmental Science and Engineering, Nankai University, Tianjin, China;2. National Academy for Mayors of China, Beijing, China;3. Hohhot Environmental Monitoring Center, China;4. Department of Chemical and Environmental Engineering, University of California Riverside, Riverside, CA, USA;5. Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA;6. School of Architecture, Civil and Environmental Engineering, École Polytechnique Fédérale de Lausanne, Lausanne, CH-1015, Switzerland;7. School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA, USA;1. Institute for Environmental and Climate Research, Jinan University, Guangzhou 511443, China;2. Guangdong Provincial Observation and Research Station for Atmospheric Environment and Carbon Neutrality in Nanling Forests, China;3. Department of Ophthalmology, The First Affiliated Hospital, Jinan University, Guangzhou, China;4. JNU–QUT Joint Laboratory for Air Quality Science and Management, Jinan University, Guangzhou 511443, China;5. International Laboratory for Air Quality and Health, Queensland University of Technology, Brisbane 4001, Australia |
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| Abstract: | Fog was sampled at four locations in California’s San Joaquin Valley (SJV) during December 1995 and January 1996 as part of the 1995 Integrated Monitoring Study (IMS95). The fog sampling campaign was conducted in two phases. During the first phase, fog was sampled at three southern SJV surface locations, two urban (Fresno and Bakersfield) and one rural (near the Kern Wildlife Refuge). Both bulk samples (representative of the entire fog drop spectrum) and size-fractionated samples were collected. During the second phase, bulk fog samples were collected at three elevations on a 430 m television transmission tower in the northern SJV, representing some of the first observations of vertical variations in fog composition. SJV fog was observed to be consistently alkaline. The median pH measured in the southern SJV was 6.49, with a range from 4.97 to 7.43. Dominant species in the fog water were ammonium (median southern SJV concentration of 1008 microequivalents/l (μN)), nitrate (483 μN), sulfate (117 μN), acetate (117 μN), formate (63 μN), and formaldehyde (46 μM). Concentrations of the inorganic ions were similar in the urban and rural fogs, although occasionally much higher spikes of S(IV) and sulfate were observed in Bakersfield fog. Acetate, formaldehyde, and total organic carbon, by contrast, were observed to be present in greater concentration in the urban fogs. Bakersfield IMS95 fog concentrations of most species were similar to those measured there in the early 1980s, although concentrations of S(IV) and sulfate were much lower in IMS95 fogs. Significant differences were found between the composition of large and small fog drops, with pH differences at times exceeding one pH unit. The chemical heterogeneity present among SJV fog drop populations is likely to result in significant enhancement of aqueous sulfate production rates over those expected from average fog properties. Significant vertical variations were also observed in fog composition. Liquid water content was observed to increase strongly with elevation, while major ion aqueous concentrations in fog drops decreased with altitude. The total amount of solute contained within the fog (per unit volume of air) was observed to increase with altitude. These observations form a unique data set to be used for model evaluation and for further analysis of aerosol processing by fogs. |
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