Free and combined amino compounds in atmospheric fine particles (PM2.5) and fog waters from Northern California

Atmospheric fine particles (PM2.5) collected during August 1997–July 1998 and wintertime fog waters collected during 1997–1999 at Davis, California were analyzed for free and combined amino compounds. In both PM2.5 and fog waters, the average concentrations of combined amino compounds (CAC, e.g., proteins and peptides) were generally 4–5 times higher than those of free amino compounds (FAC, i.e., amino acids and alkyl amines). Concentrations of total amino compounds (TAC=FAC+CAC) ranged from 1260 to 3650 pmol m−3 air in PM2.5, and from 1620 to 5880 pmol m−3 air in fog waters. Average values (±1σ) were 2500±879 and 3400±1430 pmol m−3 air, respectively. Concentrations of amino compounds in PM2.5 varied seasonally, with a peak during late winter and early spring. Ornithine was a major FAC component in both PM2.5 and fog waters (typically accounting for ∼20% of FAC), but these sample types otherwise had fairly different FAC distributions. FAC in PM2.5 were enriched in protein-type amino species such as glycine/threonine, serine and alanine, while fog water FAC had significantly higher levels of non-protein species such as methylamine, γ-aminobutyric acid and ethanolamine. The compositions of CAC in PM2.5 and fogs were fairly similar and were mainly protein-type. Mass concentrations of TAC in PM2.5 and fog waters were, on average, 302 and 399 ng m−3 air, respectively. Amino compounds were an important component of the organic carbon pool for both fog and particles, with TAC accounting for an average of 13% of the dissolved organic carbon in fog waters and ∼10% of the water-soluble organic carbon in PM2.5. At these levels amino compounds likely play important roles in the chemistry of fog drops and fine particles, for example by influencing their buffering capacity and basicity.