The distribution of aerosol nitrate compounds with respect to particle size: vaporization analysis with the low pressure impactor

The atmospheric aerosol was sampled with a low pressure impactor at a coastal, an urban, and an agricultural site in the Los Angeles air basin. The material collected on each stage was analyzed for nitrate by direct vaporization into a chemiluminescent analyzer, sensitive at nanogram levels. The method responds to inorganic nitrate compounds which vaporize or decompose below about 1200°C. The coastal nitrate size distribution consists mainly of particles which have diameters greater than 2.0 µM, whereas the nitrate in the agricultural region is found primarily in the submicron range. The urban location, exhibiting characteristics of both coastal and agricultural regions, was bimodal about the 1-2 µm range. It is believed that the submicron aerosol is ammonium nitrate while the larger size fraction is sodium nitrate