During June 1986, eight systems for measuring vapor phase and four for measuring particulate phase concentrations of formic acid (HCOOH) and acetic acid (CH3COOH) were intercompared in central Virginia. HCOOH and CH3COOH vapors were sampled by condensate, mist, Chromosorb 103 GC resin, NaOH-coated annular denuders, NaOH impregnated quartz filters, K2CO3 and Na2CO3 impregnated cellulose filters, and Nylasorb membranes. Atmospheric aerosol was collected on Teflon and Nuclepore filters using both hi-vol and 10-vol systems to measure particulate phase concentrations. Samples were collected during 31 discrete day and night intervals of 0.5-2 hour duration over a 4-day period. Performance of the mist chamber and K2CO3 impregnated filter techniques were also evaluated using zero air and ambient air spiked with HCOOHg, CH3COOHg , and formaldehyde (CH2Og) from permeation sources. Results of this intercomparison show significant systematic and episodic artifacts among many currently deployed measurement systems for HCOOHg and CH3COOHg. The spiking experiments revealed no significant interferences for the mist chamber technique and results generated by the mist chamber and denuder techniques were statistically indistinguishable. The condensate technique showed general agreement with the mist chamber and denuder methods, but episodic bias between these systems was inferred from large and significant differences observed during the first day of sampling. Nylasorb membranes are unacceptable for collecting carboxylic acid vapors as they did not retain HCOOHg and CH3COOHg quantitatively.Strong base impregnated filter and GC resin sampling techniques are prone to large positive interferences apparently resulting, in part, from reactions involving CH2Og to generate HCOOH and CH3COOH subsequent to collection. Significant bias presumably associated with differences in postcollection handling was observed for particulate phase measurements by participating groups. Analytical bias did not contribute significantly to differences in vapor and particulate phase measurements.

Measurement of the background levels and study of the chemistry of trace organic carbon species in the remote marine troposphere occurred during an April-July 1987 SAGA II cruise in remote regions of the Pacific and Indian Oceans. Measured compounds included carboxylic acids, formaldehyde, light hydrocarbons (C2-C4), and ozone. The results show seasonal, diel, and spatial dependencies for the organic acids. Distinct latitudinal gradients are seen for most sampled compounds. Formic acid is well correlated with suspected precursors, formaldehyde and light hydrocarbons. Acetic acid follows a similar pattern as formic acid, although its precursors are as yet undefined. Did patterns of low amplitude for the organic acids in the remote marine troposphere suggest a natural contribution to tropospheric photochemistry, and to the global carbon cycle as well. For the northern hemisphere Pacific Ocean, the mean formic acid mixing ratio was 0.80 + 0.30 ppbv, the mean acetic acid value was 0.78 + 0.32 ppbv. For the southern hemisphere Pacific Ocean, formic acid averaged 0.22 + 0.13 ppbv, for acetic acid, the mean was 0.28 +_ 0.18 ppbv. For the northem hemisphere Indian Ocean, the mean formic acid mixing ratio was 0.75 + 0.24 ppbv, and the mean acetic acid value was 0.69 + 0.27 ppbv. For the southern hemisphere Indian Ocean, the mean formic acid value was 0.19 + 0.17 ppbv, and the mean acetic acid value was 0.29 + 0.16 ppbv. Highest levels of organic acids were encountered near known anthropogenic source regions, in air masses of continental origin, or near regions of naturally produced alkenes (C 2, C3). The ozone-alkene oxidation scheme appears to play a major role in gas phase organic acid production in the remote marine troposphere. Nighttime gas phase deposition of the organic acids onto the ocean surface appears to be a major sink. 2Now at College of Sciences, University of Maine, Orono. in the gas phase. Analogous aqueous-phase reactions leading 3Now at NOAA, GMCC Samoa Observatory, Pago Pago, American Samoa. to the production of acetic acid are recognized as being 4Now at Joint Institute for the Study of the Atmosphere and Ocean, negligibly slow [Jacob and Wofsy, 1988a] and therefore not a University of Washington, Seatfie. significant source. Such reactions are also limited by the lower solubility of acetaldehyde. Predicted gas-phase formic acid mixing ratios calculated from aqueous phase reaction Copyright 1990 by the American Geophysical Union. mechanisms are between 35 and 65 pptv [Charneides and Paper number 90JD01223. Davis, 1983]. Since it is generally agreed that aqueous-phase 0148-0227/90/90JD-01223505.00 production of organic acids alone cannot account for the 16,391 16,392 ARLANDER ET AL.: GASEOUS OXYOENATED HYDROCARBONS FTIR spectroscopic evidence for the formation of CH2(OH)OOH in D.R. Cronn, College of Sciences, University of Maine, Orono, ME the gas phase reaction of HO e with CH:O, Chem. Phys. Lett., 75, 04469. 533, 1980b. J.C. Farmer, NOAA, GMCC Samoa Observatory, Pago Pago, Norton, R. B., Measurement ...

Ozone concentrations in the atmospheric boundary layer of the Pacific and Indian Oceans were measured on four separate oceanographic research cruises (July 1986, May to August 1987, April to May 1988). These measurements show a distinct zone of near zero (≤3 ppb) ozone concentration in the central equatorial Pacific in April–May, with ozone increasing in this region over the next 4 months. The seasonal observed change in the latitudinal gradient of ozone is consistent with previous ozone measurements at Hilo and Samoa by Oltmans and Komhyr [1986] and predictions from an atmospheric general circulation model study [Levy et al., 1985]. A significant diurnal cycle of ozone was found in almost all locations with a maximum near sunrise, a minimum in the late afternoon, and a peak‐to‐peak amplitude of 1 to 2 ppb (10–20%), similar to that predicted by a photochemical model in the low NOx limit [Thompson and Lenschow, 1984].

Ambient concentrations of isoprene and several of its atmospheric oxidation productsmethacrolein, methylvinyl ketone, formaldehyde, formic acid, acetic acid, and pyruvic acid -were measured in a central Pennsylvania deciduous forest during the summer of 1988. Isoprene concentrations ranged from near zero at night to levels in excess of 30 ppbv during daylight hours. During fair weather periods, midday isoprene levels normally fell in the 5-10 ppbv range. Methacrolein and methylvinyl ketone levels ranged from less than 0.5 ppbv to greater than 3 ppbv with average midday concentrations in the 1 to 2 ppbv range. The diurnal behavior of formaldehyde paralleled that of isoprene with ambient concentrations lowest (-1 ppbv) in the predawn hours and highest (>9.0 ppbv) during the afternoon. The organic acids peaked during the midday period with average ambient concentration of 2.5, 2.0, and 0.05 ppbv for formic, acetic, and pyruvic acid, respectively. These data indicate that oxygenated organics comprise a large fraction of the total volatile organic carbon containing species present in rural, forested regions of the eastern United States. Consequently, these compounds need to be included in photochemical models that attempt to simulate oxidant behavior and/or atmospheric acidity in these forested regions.

The condensation of water vapor onto a cooled surface can be used as a method of sampling atmospheric components; the method is investigated theoretically and experimentally. From solutions to the heat and mass flow within the convective boundary layer, it is shown that the method has greatest collection efficiency for highly soluble gases. Discrimination against particulates and relatively insoluble gases should be excellent. The method is illustrated by some measurements of NH3, HNO3, HNO2, SO2, HCl, H2O2, HCHO, HCOOH, and CH3COOH in the vicinity of Tucson, Arizona. Concentrations are in the part‐per‐billion range or below. Diurnal variations in these concentrations are discussed. Explanations are offered for a discrepancy between theoretical and actual rate of collection of water vapor.