Detection of alkaline ultrafine atmospheric particles at Bakersfield, California.

Two collected micro-orifice uniform deposit impactors (MOUDIs) and a filter-based sampler were used to measure the size distribution and chemical composition of atmospheric particulate matter at Bakersfield, CA, between January 14 and 23, 1999. The peak number concentration of airborne ultrafine particles measured was 1.45 x 10(11) m-3, which is a factor of approximately 3 higher than the peak airborne ultrafine-particle number concentration measured previously in Pasadena, CA. Chemical analysis revealed that airborne ultrafine particles (Dp < 0.1 micron) at Bakersfield contained significant amounts of water-soluble species, including calcium, sodium, ammonium ion, nitrate, and sulfate. Other chemical species detected in the ultrafine size range included potassium, iron, copper, zinc, and strontium. A balance of aqueous ions showed that ultrafine particles were alkaline in nature with calcium acting as the dominant cation. Bulk samples of airborne particles with diameter less than 2.0 microns (PM2.0) were essentially neutral, but particle acidity was found to be a strong function of particle size. The results of this experiment suggest that areas deep in the human lung that preferentially collect particles in the ultrafine size range could be exposed to locally acidic or alkaline conditions even if the integrated airborne particle complex is essentially neutral.