Atmospheric geochemistry of formic and acetic acids at a mid‐latitude temperate site

Abstract

We have determined the atmospheric concentrations of formic and acetic acid in gas and particulate phases and in precipitation over a 15-month time period at a site in eastern Virginia. These atmospheric species occurred principally in the gas phase (•>98%), with a marked annual seasonality. Atmospheric concentrations of formic and acetic acid in the gas phase averaged 1890 ___ 1235 and 1310 ___ 910 ppt during the growing season, compared to 695 ___ 405 and 700 _+ 375 ppt over the nongrowing season, respectively. Our data support the hypothesis that biogenic emissions from vegetation are important sources of atmospheric formic and acetic acid during the local growing season. The same general time series trends were also evident in precipitation, but the seasonality was not defined nearly as well as in the gas phase. Atmospheric concentrations of aerosol formate and acetate showed substantial temporal variability and generally remained in the 5-to 25-ppt range throughout the year. Our measurements indicate that the near-surface (< 10 m altitude) diurnal behavior of formic and acetic acids in the gas phase is as follows: the concentrations are lowest prior to sunrise, increase steadily thereafter, and begin to decline by late afternoon, again reaching very low levels in the early morning hours. We have observed a diurnal variation with an amplitude of up to tenfold in atmospheric concentration for formic acid. This pronounced diurnal variation is presumably related to mixed layer dynamics, in addition to daytime biogenic and photochemical source inputs and gaseous dry deposition at nighttime. The removal of organic acids from the nocturnal boundary layer may be facilitated by uptake of their vapors into dew. A striking feature of our data is the distinct differences in both gas phase and precipitation ratios of formic-to-acetic acid between the growing and nongrowing seasons. In the gas phase this ratio had a mean value of 1.33 during the growing season, decreasing to 0.90 in the nongrowing season. Likewise, the ratio averaged 1.43 and 1.09 in precipitation at this site during the growing and nongrowing season, respectively. Our measurements indicated that direct emissions from motor vehicles and biomass combustion processes are important sources of atmospheric acetic acid and that these sources have formicto-acetic ratios much less than 1.0. We hypothesize that the seasonal variability in formic-to-acetic acid ratios in ambient air is due to a shift in the relative dominance of biogenic versus anthropogenic sources. During the nongrowing season, anthropogenic inputs appear to be the principal source of acetic acid to the atmosphere. However, it remains unclear as to what the major source of formic acid is to the wintertime atmosphere. 1988a]. Carboxylic acids are also common constituents of global precipitation [Galloway et al., 1982-1, with formic and acetic acids generally constituting the majority of the free acidity in remote regions [Keene et al., 1983; Keene and Galloway, Paper number 7D0900. 0148-0227/88/00...

Chemical characteristics and sources of organic acids in precipitation at a semi-urban site in Southwest China

“…These organic acids contribute significantly to rainwater acidity in urban areas (Fornaro and Ivano, 2003;Kawamura et al, 2001;Pena et al, 2002;Sakugawa et al, 1993) and account for as much as 80e90% of the acidity in remote areas of the world (Andreae et al, 1988;Keene and Galloway, 1986). Direct anthropogenic emissions (Kawamura et al, 1985;Talbot et al, 1988) and biogenic emissions as well as secondary sources like in situ production from precursors in the troposphere (Madronich et al, 1990;Orzechowska and Paulson, 2005) have been suggested as their major sources in the atmosphere. In spite of the important role of carboxylic acids in the atmosphere, few studies have been performed on the variation of organic acids in acid rain in China.…”

Sampling of organic volatiles in the atmosphere at moderate and low pollution levels

“…However, intercomparison experiments [107] have shown that substantial artefacts for formic acid can be caused by sampling on alkaline filters. Such artefacts are not observed with denuder or mist chamber sampling [108]. Another advantage of denuder-type samplers is the separation between the gas and particle phases without the use of filters which might cause further interferences.…”

Urban and rural observations of carboxylic acids in rainwater in Southwest of China: the impact of urbanization

“…Many studies have been conducted to understand the diurnal variations of the acids in gas phase (Talbot et al 1988). However, to the best of our knowledge, few studies have been addressed to their diurnal cycles in rainwater (Avery et al 2001a, b).…”

“…On the contrary, the gas phase F/A ratio is more than 1 in Guiyang which may be caused by secondary sources in the atmosphere (Jordan et al 2009). Biomass burning 0.1∼0.5 (Talbot et al 1988) 0.2∼0.4 (Hartmann et al 1991) Vehicular emissions 0.4∼0.6 (Talbot et al 1988) 0.3∼0.5 (Grosjean 1992) Vegetation (tropical forests) 0.6 (Talbot et al 1990) Vegetation emissions 0.4 (Servant et al 1991) Secondary sources >1 (Talbot et al 1988) The unsaturated hydrocarbons (olefins, isoprene) are important factor to control the concentrations of carboxylic acids in the atmosphere which may originate from biogenic or anthropogenic sources (Lee et al 2006). …”