* Corresponding author. Tel.: #1-530-752-1213; fax: #1- 530-752-4107. E-mail address: baholmen@ucdavis.edu (B.A. Holme H n). Atmospheric Environment 35 (2001) 3251} 3264 Lidar-assisted measurement of PM  emissions from agricultural tilling in California's San Joaquin Valley } Part I: lidar Britt A. Holme H n*, Teresa A. James, Lowell L. Ashbaugh, Robert G. Flocchini Air Quality Group, Crocker Nuclear Laboratory, University of California, Davis, CA 95616, USA Received 25 April 2000; accepted 31 October 2000 Abstract Vertical pro"ling with point samplers is an accepted method for quantifying the #uxes of PM  from non-point fugitive dust sources, but is limited by uncertainty in estimates of the actual height of the dust plume, especially for plumes that exceed the highest sampling height. Agricultural land preparation operations in the San Joaquin Valley were monitored using upwind}downwind vertical PM  pro"les and data collected during the "rst successful experiment to include light detection and ranging (lidar), in 1998, were analyzed to provide modeling criteria for the 1996 and 1997 data. A series of six comprehensive PM  tests with concurrent lidar data was examined to: (a) develop a framework for analyzing upwind}downwind point PM  concentration pro"les of land preparation operations (disking, listing, root cutting, and ripping) and (b) identify conditions under which the "eld sampling strategies a!ect the reproducibility of PM  concentration measurements. Lidar data were used to verify that the plume heights and shapes extrapolated from the point sampler vertical pro"les adequately described the plumes. The shortcomings of the vertical pro"ling technique and lidar methods are discussed in the light of developing e$cient robust methods for accurate PM  emissions quanti"cation from complex non-point sources.  2001 Elsevier Science Ltd. All rights reserved. Keywords: PM10, Lidar; Plume height; Agricultural dust; Nonpoint sources 1. Introduction In late summer and fall, a large fraction ( ' 50%) of the PM  in California's San Joaquin Valley (SJV) has been attributed to primary geologic material, generally soil dust (Chow et al., 1990, 1992). This material becomes airborne by suspension of surface soils during wind ero- sion, agricultural activities, tra$c on paved and unpaved roads, and construction activity. Late summer and fall PM  standard violations (Dolislager and Motallebi, 1999) coincide with the harvest season of many Califor- nia crops (e.g., cotton, almonds, tomatoes), suggesting that agricultural activities (both harvesting and sub- sequent land preparation) may be signi"cant sources of PM  during this time of year. Potential e!orts to con- trol this component of PM  require accurate quanti"ca- tion of these sources, but little information has been available to date to estimate PM  emissions from SJV agricultural activities. Since 1991, the University of California has collected PM  emissions data from a wide range of agricultural activities in the SJV. Current techniques use (a) up- wind/downwind vertical pro"les of wind speed and PM concentrations (PM  and PM  ) to quantify PM emis- sion factors and (b) lidar vertical scans to verify plume heights and pro"le shapes. The PM point sampling techniques draw on observations made by previous fugitive dust researchers using upwind/downwind arrays (Cowherd et al., 1974; Flocchini et al., 1994), exposure pro"ling (Cowherd et al., 1974; Cuscino et al., 1984; Flocchini et al., 1994), high-volume "ltration samplers 1352-2310/01/$- see front matter  2001 Elsevier Science Ltd. All rights reserved. PII:S1352-2310(00)00518-5