No abstract

The 14‐month‐long (December 1999 to February 2001) Central California Regional PM10/PM2.5 Air Quality Study (CRPAQS) consisted of acquiring speciated PM2.5 measurements at 38 sites representing urban, rural, and boundary environments in the San Joaquin Valley air basin. The study's goal was to understand the development of widespread pollution episodes by examining the spatial variability of PM2.5, ammonium nitrate (NH4NO3), and carbonaceous material on annual, seasonal, and episodic timescales. It was found that PM2.5 and NH4NO3 concentrations decrease rapidly as altitude increases, confirming that topography influences the ventilation and transport of pollutants. High PM2.5 levels from November 2000 to January 2001 contributed to 50–75% of annual average concentrations. Contributions from organic matter differed substantially between urban and rural areas. Winter meteorology and intensive residential wood combustion are likely key factors for the winter‐nonwinter and urban‐rural contrasts that were observed. Short‐duration measurements during the intensive operating periods confirm the role of upper air currents on valley‐wide transport of NH4NO3. Zones of representation for PM2.5 varied from 5 to 10 km for the urban Fresno and Bakersfield sites, and increased to 15–20 km for the boundary and rural sites. Secondary NH4NO3 occurred region‐wide during winter, spreading over a much wider geographical zone than carbonaceous aerosol.

No abstract

PM,, (particles < 10 y m in aerodynamic diameter) and PM,,, (particles < 2.5 y m in aerodynamic diameter) mass, elements, water-soluble nitrate, sulfate, ammonium, sodium, potassium, and organic and elemental carbon were determined in 24-h aerosol samples collected during this period. Federal and state standards for PM,, were exceeded a t both urban and nonurhan sites. PM,, concentrations were generally highest during winter and were dominated by PM,, during this time. The coarse (PM1, minus PM,.,) aerosol fraction constituted more than half of PM,, mass during the summer and fall.PM,, concentrations of secondary ammonium nitrate were elevated during the winter a t all sites. Conversely, concentrations of coarse particle iron, indicative of geologically related dust, were higher under less humid conditions during the summer and fall. Regionwide meteorological and chemical transformation processes influence the secondary (nitrate and sulfate) components of PM,,. Elevated concentrations of coarse-particle dust, however, appear to originate from local emissions, such as agricultural and transportation-related activities, as well as region-wide emissions.

UNMIX and Positive Matrix Factorization (PMF) solutions to the Chemical Mass Balance (CMB) equations were applied to chemically speciated PM2.5 measurements from 23 sites in California's San Joaquin Valley to estimate source contributions. Six and seven factors were determined by UNMIX for the low_PM2.5 period (February to October) and high_PM2.5 period (November to January), respectively. PMF resolved eightfactors for each period that corresponded with the UNMIX factors in chemical profiles and time series. These factors are attributed to marine sea salt, fugitive dust, agriculture-dairy, cooking, secondary aerosol, motor vehicle, and residential wood combustion (RWC) emissions, with secondary aerosol and RWC accounting for over 70% of PM2.5 mass during the high_PM2.5 period. A zinc factor was only resolved by PMF. The contribution from motor vehicles was between 10 and 25% with higher percentages occurring in summer. The PMF model was further evaluated by examining (1) site-specific residuals between the measured and calculated concentrations, (2) comparability of motor vehicle and RWC factors against source profiles obtained from recent emission tests, (3) edges in bi-plots of key indicator species, and (4) spatiotemporal variations of the factors' strengths. These evaluations support the compliance with model assumptions and give a higher confidence level to source apportionment results for the high_PM2.5 period.