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...

[1] In the biomass, soils, and peatlands of Siberia, boreal Russia holds one of the largest pools of terrestrial carbon. Because Siberia is located where some of the largest temperature increases are expected to occur under current climate change scenarios, stored carbon has the potential to be released with associated changes in fire regimes. Our concentration is on estimating a wide range of current and potential emissions from Siberia on the basis of three modeled scenarios. An area burned product of Siberia is introduced, which spans from 1998 through 2002. Emissions models are spatially explicit; therefore area burned is extracted from associated ecoregions for each year. Carbon consumption estimates are presented for 23 unique ecoregions across Siberia, which range from 3.4 to 75.4 t C ha À1 for three classes of severity. Total direct carbon emissions range from the traditional scenario estimate of 116 Tg C in 1999 (6.9 M ha burned) to the extreme scenario estimate of 520 Tg C in 2002 (11.2 M ha burned), which are equivalent to 5 and 20%, respectively, of total global carbon emissions from forest and grassland burning. Our results suggest that disparities in the amount of carbon stored in unique ecosystems and the severity of fire events can affect total direct carbon emissions by as much as 50%. Additionally, in extreme fire years, total direct carbon emissions can be 37-41% greater than in normal fire years, owing to increased soil organic matter consumption. Mean standard scenario estimates of CO 2 (555-1031 Tg), CO (43-80 Tg), CH 4 (2.4-4.5 Tg), TNMHC (2.2-4.1 Tg), and carbonaceous aerosols (4.6-8.6 Tg) represent 10, 15, 19, 12 and 26%, respectively, of the global estimates from forest and grassland burning. Accounting for smoldering combustion in soils and peatlands results in increases in CO, CH 4 , and TNMHC and decreases in CO 2 emitted from fire events.

Abstract. Meteorological conditions, extremely conducive to fire development and spread in the spring of 1987, resulted in forest fires burning over extremely large areas in the boreal forest zone in northeastern China and the southeastern region of Siberia. The great China fire, one of the largest and most destructive forest fires in recent history, occurred during this period in the Heilongjiang Province of China. Satellite imagery is used to examine the development and areal distribution of 1987 forest fires in this region. Overall trace gas emissions to the atmosphere from these fires are determined using a satellite-derived estimate of area burned in combination with fuel consumption figures and carbon emission ratios for boreal forest fires.

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