Comparison of Particle Light Scattering and Fine Particulate Matter Mass in Central California

AbstractParticle light scattering (Bsp) from nephelometers and fine particulate matter (PM2.5) mass determined by filter samplers are compared for summer and winter at 35 locations in and around California’s San Joaquin Valley from December 2, 1999 to February 3, 2001. The relationship is described using particle mass scattering efficiency (σsp) derived from linear regression of Bspon PM2.5that can be applied to estimated PM2.5from nephelometer data within the 24-hr filter sampling periods and between the every-6th-day sampling frequency. An average of σsp=4.9 m2/g was found for all of the sites and seasons; however, σspaveraged by site type and season provided better PM2.5estimates. On average, the σspwas lower in summer than winter, consistent with lower relative humidities, lower fractions of hygroscopic ammonium nitrate, and higher contributions from fugitive dust. Winter average σspwere similar at non-source-dominated sites, ranging from 4.8 m2/g to 5.9 m2/g. The σspwas 2.3 m2/g at the roadside, 3.7 m2/g at a dairy farm, and 4.1 m2/g in the Kern County oilfields. Comparison of Bspfrom nephelometers with and without a PM2.5inlet at the Fresno Super-site showed that coarse particles contributed minor amounts to light scattering. This was confirmed by poorer correlations between Bspand coarse particulate matter measured during a fall sampling period.