Reveal: Characterizing fine aerosols in the Fraser Valley, B.C.

Abstract

The REVEAL field study was conducted during July and August 1993 to document the chemical and physical characteristics of ambient fine aerosols in southwestern British Columbia (B.C.) (particularly the Lower Fraser Valley (LFV)) and to quantify the impact of those aerosols upon visibility in the LFV. A description of the study motivations, objectives and monitoring protocols are presented herein along with results of analyses conducted using the REVEAL datasets. It is shown that: visibility and aerosol concentrations/composition are highly variable in the temporal and spatial dimensions, and while organic matter dominates fine aerosol mass (accounting for 35–46% of the mean fine aerosol mass) in the LFV, nitrate and sulphate dominate particle light scattering (bsp) (accounting for 55–67% of mean bsp) in this region. The severity of visibility impairment in the valley despite comparatively low fine mass concentrations is attributed to the high mass scattering efficiencies of the ambient aerosols (due in part to the relative abundance of ammonia/ium). Source types of ambient fine aerosols at four of the monitoring sites are identified using Principal Components Analysis (PCA), and used to calculate first approximations of mass contributions by source type using regression analysis. Results indicate that direct vehicle emissions, secondary aerosols and soil/road dust dominate the sources of fine aerosols in the LFV. Analysis of supplementary data indicates that the REVEAL monitoring period was characterized by fairly typical summertime visibility and meteorological conditions for the region and hence that it is possible to generalize from these analyses. The gross spatial features of the secondary fine aerosol distribution in the LFV are explained in relation to the prevailing meteorology and spatial patterns of precursor emissions.