Wintertime particulate matter in the San Joaquin Valley: Concentrations, mechanisms and sources

In this dissertation measurements of size segregated PM made during the period Dec 16th, 2000--Feb 3rd, 2001 at 5 locations near or within the San Joaquin Valley are discussed: Bodega Bay, Davis/Sacramento, Modesto, Bakersfield, and Sequoia National Park. Fine airborne particle (PM 1.8) concentrations at the most heavily polluted site (Bakersfield) increased from 20 mug m-3 to 172 mug m-3 during the period Dec 16th, 2000--Jan 7th, 2001. The majority of the fine particle mass was ammonium nitrate driven by an excess of gas-phase ammonia. Peak ultrafme particle (PM0.1) concentrations (8--12hr average) were approximately 2.4 mug m-3 measured at night in Sacramento and Bakersfield. Ultrafine particle concentrations were distinctly diurnal with daytime concentrations approximately 50% lower than nighttime concentrations. The majority of the ultrafine particle mass was associated with carbonaceous material. Analysis of size segregated airborne PM measured revealed two distinct types of airborne particles based on diurnal patterns and size distribution similarity: hygroscopic sulfate/ammonium/nitrate particles and less hygroscopic particles composed of mostly organic carbon with smaller amounts of elemental carbon. The hygroscopic particles had a mass distribution peak in the accumulation mode (0.56--1.0 mum) at all times while the carbon particle mass distribution varied between 0.2--1.0 mum. The analysis suggests that carbon particles and sulfate/ammonium/nitrate particles exist separately in the atmosphere of the San Joaquin Valley until coagulation mixes them in the accumulation mode.; To measure transition metals in the size segregated collected samples, a new method was developed using acetone extraction followed by inductively coupled plasma mass spectrometry. The coarse fraction is dominated by elements indicative of windblown dust. These elements covaried with the secondarily formed ammonium nitrate particles over the stagnation event. In the fine fraction the dominant clusters were those indicative of wood-burning in the form of rubidium - potassium - organic and elemental carbon. Other elements that covaried with the directly emitted carbonaceous particles include cadmium, barium, lead, elements more likely indicative of transportation. In the ultrafine fraction the only cluster observed was rubidium and potassium. These elements stem from wood burning. The transition metals with highest concentrations in the ultrafine mode include iron and magnesium.