Spatial representativeness and scales of transport during the 1995 Integrated Monitoring Study in California's San Joaquin Valley

Daily measurements of PM10 mass and chemical composition were obtained for the period 1-14 November 1995 from a saturation monitoring network around C orcoran, and for varying portions of the period 9 December 1995-6 January 1 996 for three networks around Bakersfield, Fresno, and the Kern Wildlife Re fuge, in California's San Joaquin Valley. During the latter period, monitor ing locations were also operated along the boundaries and across the width of the Valley. The Corcoran, Bakersfield, and Fresno networks consisted of 12-25 sites, located in areas of about 300-800 km(2). Each network also inc luded one con site, situated at a pre-existing monitoring location, with mo re extensive and more temporally resolved measurements. Mean concentrations of PM10 and its constituents varied from core-site concentrations by 20% o r more over distances ranging from 4 to 14 km. Local source influences were observed to affect sites over distances of less than I km, but primary par ticulate emissions were also transported over urban or sub-regional scales of approximately 10-30 km during the winter and greater than 30 km in the f all. During winter, gas-phase precursors of secondary aerosol may have been transported over distances of approximately 100 km, but little evidence wa s found for transport of primary PM on such a scale. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.