Seasonal and Spatial Characteristics of Formic and Acetic Acids Concentrations in the Southern California Atmosphere

Abstract

Formic and acetic acids measurements made during the year 1986 are reported for eight sites in the Los Angeles basin and one remote offshore site. Formic and acetic acids concentrations measured in marine air upwind of the Los Angeles area over an 8-month period average 1.4 and 0.6 ppb, respectively, while concentrations within the Los Angeles urban area average 2.7−5.8 ppb formic acid and 2.9−4.2 ppb acetic acid. Average formic and acetic acids concentrations exceed average HNO3 and HCl concentra tions, making them the most abundant gas phase acids in the southern California atmosphere throughout the year. Formic and acetic acids concentrations near the coast change in proportion to changes in atmospheric dilution potential, as would be expected if formic and acetic acids were emitted directly from widespread area sources such as motor vehicle traffic. Downwind of Los Angeles, formic and acetic acids concentrations peak during the summer photochemi cal smog season, and concentration changes track both changes in atmospheric oxidant concentrations and markers for heterogeneous conversion within clouds or fog. Formic and acetic acids concentrations thus appear to arise both from direct emissions and from atmospheric chemical production, with the relative importance of these pathways varying spatially over the area surveyed.

Emissions and photochemistry of oxygenated VOCs in urban plumes in the Northeastern United States

“…5 were filtered to eliminate the biomass fire plumes and that the emission ratio for acetic acid is assumed to be zero in this work (de Gouw et al, 2005). This suggests that the discrepancy between the model and the measurements may be attributed either to missing direct emissions (likely biogenic) or to an unknown gas-phase or heterogeneous production mechanism (Nolte et al, 1997;Turpin et al, 2006).…”

Enhanced formation of formate by freezing in solutions of hydrated formaldehyde-metal-hydrogen peroxide

“…Formic acid (HCOOH) is a commonly found organic acid in the environment (Kawamura et al, 1985;Nolte et al, 1997) and it controls the acidity of cloud and rain in pristine regions of the troposphere (Chameides and Davis, 1983;Jacob, 1986;Andreae et al, 1988). At remote locations, formate concentrations of (1-10) µM were observed (Galloway et al, 1982).…”

Levoglucosano e íons solúveis em água no material particulado atmosférico MP10 e MP2,5. caracterização de sítios Sul-Americanos

“…FIGURA 4 -Estruturas dos compostos provenientes da combustão da celulose: levoglucosano e seus estereoisômeros (Extraído e adaptado de Schkolnik e Rudich, 2006) A concentração destes ácidos orgânicos tem aumentado em áreas urbanas quando comparados a áreas remotas, portanto, apresentam um importante papel na determinação da acidez de precipitação, da acidez de fumaça e orvalho, e o fluxo de deposição seca de ácidos em regiões urbanizadas (Nolte et al, 1997).…”

“…Estes compostos são ubíquos nas fases gasosas e aquosas da troposfera, e presentes também no aerossol atmosférico, contribuindo para o aumento da acidez da chuva (Nolte et al, 1997;Wang et al, 2007). As emissões diretas (queima da biomassa, exaustão veicular) são as fontes destes compostos em regiões urbanas e industriais (Chebbi e Carlier, 1996 , formiato e acetato).…”

“…Diversos desses compostos são reativos e exercem um papel importante na química da troposfera, afetando a qualidade do ar, o balanço regional e global de oxidantes em regiões urbanizadas (Nolte et al, 1997).…”