Copyright 2005 Air & Waste Management Association Size and Composition Distribution of Airborne Particulate Matter in Northern California: I—Particulate Mass, Carbon, and Water-Soluble Ions

Abstract

The San Joaquin Valley (SJV) in California has one of the most severe particulate air quality problems in the United States during the winter season. In the current study, measurements of particulate matter (PM) smaller than 10 [H9262]m in aerodynamic diameter (PM₁₀), fine particles (PM_1.8), and ultrafine particles (PM_0.1) made during the period December 16, 2000–February 3, 2001, at six locations near or within the SJV are discussed: Bodega Bay, Davis, Sacramento, Modesto, Bakersfield, and Sequoia National Park. Airborne PM_1.8 concentrations at the most heavily polluted site (Bakersfield) increased from 20 to 172 [H9262]g/m³ during the period December 16, 2000–January 7, 2001. The majority of the fine particle mass was ammonium nitrate driven by an excess of gas-phase ammonia. Peak PM_0.1 concentrations (8–12 hr average) were [H11011]2.4 [H9262]g/m³ measured at night in Sacramento and Bakers-field. Ultrafine particle concentrations were distinctly diurnal, with daytime concentrations [H11011]50% lower than nighttime concentrations. PM_0.1 concentrations did not accumulate during the multiweek stagnation period; rather, PM_0.1 mass decreased at Bakersfield as PM_1.8 mass was increasing. The majority of the ultrafine particle mass was associated with carbonaceous material. The high concentrations of ultrafine particles in the SJV pose a potential serious public health threat that should be addressed.