Second generation chemical mass balance source apportionment of sulfur oxides and sulfate at the Grand Canyon during the Project MOHAVE summer intensive

Receptor-based chemical mass balance (CMB) analysis techniques are designed to apportion species that are conserved during pollutant transport using c onserved source profiles. The techniques will fail if non-conservative spec ies (or profiles) are not properly accounted for in the CMB model. The stra ightforward application of the CMB model developed for Project MOHAVE using regional profiles resulted in a significant under-prediction of total sulf ate oxides (SOx, SO2 plus fine particulate sulfate) for many samples at Mea dview, AZ. In addition, for these samples the concentration of the inert tr acer emitted from the MOHAVE Power Project (MPP), ocPDCH, was also underpre dicted. A second-generation model has been developed which assumes that sep aration of particles and SO2 can occur in the MPP plume during nighttime st able plume conditions. This second-generation CMB model accounts for all SO x present at the various receptor sites. In addition, the concentrations of ocPDCH and the presence of other inert tracers of emission from regional s ources are accurately predicted. The major source of SOx at Meadview was th e MPP, but the major source of sulfate at this site was the Las Vegas urban area. At Hopi Point in the Grand Canyon, the Baja California region (Imper ial Valley and northwestern Mexico) was the major source of both SOx and su lfate.