Total Anthropogenic Suspended Particulate as Derived from Chemical Analysis of Chloride and Silicate on High-Volume Samples

Abstract

Extensive chemical analysis of suspended particulate was undertaken by the Bay Area Air Pollution Control District, so that more meaningful interpretation of total mass loading data could be made and more serious problem areas detected. From high-volume samples taken with cellulose paper as the collection medium, analyses were performed for the five heavy metals and nitrate, sulfate, chloride, silicon, and total organics (loss on ignition at 550°C).

Two constituents considered primarily nonanthropogenic, silicate and chloride, were evaluated from eight sampling sites. The data were derived from over 600 individual samples, one sample per week per site. The locations have diverse geographical backgrounds, although they lie in a common air basin. For example, a 21 month average for chlorides ranged from 4.2 µ/m³ at San Francisco to 1.7 µg/m³ at Livermorè some 40 miles inland. Inversely, the total silicates increased from 5.7 µg/m³ at San Francisco to 22.6 µg/m³ at Livermore. The silicate values peak strongly in the dry season, with individual 24 hr silicate component values greater than 60 µg/m³ at inland stations. Wind-generated dust from the bare hills of the Coast Range is the most probable source.

Since the silicates and chlorides are primarily non-anthropogenic, they were excluded from the TSP values to give a total anthropogenic suspended particulate (TASP). The TASP values for the Bay Area show a geographic distribution in much closer conformity to visibility reduction and citizen complaint than do TSP values.