Atmospheric chemistry and distribution of formaldehyde and several multioxygenated carbonyl compounds during the 1995 Nashville/Middle Tennessee Ozone Study

Abstract

Abstract. Airborne measurements of formaldehyde (FA), glycolaldehyde (GA), glyoxal (GL), methylglyoxal (MG), and pyruvic acid (PD) were made on board instrumented aircraft platforms, the Department of Energy G 1 and National Oceanic and Atmospheric Administration P3 (FA only), during the 1995 Nashville/Middle Tennessee Ozone Study. FA data determined on these two aircraft during three intercomparison flights agreed to within-10%. The mean and median (in parentheses) concentrations observed within the boundary layer (< 2000 m) for FA, GA, GL, MG, and PD were 4.2 (3.9), 0.78 (0.70), 0.07 (0.06), 0.14 (0.10), and 0.24 (0.23), respectively (all in parts per billion by volume (ppbv)). At the observed concentrations, FA accounted for a substantial fraction of the OH reactivity, comparable to isoprene and CO. Further, it served as an important free radical precursor, contributing 25-30% of the radical production during midday and even greater during morning and late afternoon periods. Source attribution of FA was assessed using measured concentrations of hydrocarbons, their reaction kinetics with the OH radicals, and FA yields. The results showed that isoprene was the dominant source of FA, responsible for-67%, methane and peroxyacetyl nitrate contributed equally at-13% each, and alkanes and alkenes which are largely of anthropogenic origin accounted for only-7%. This assessment based on reaction kinetics is consistent with the strong correlations (r > 0.8) observed between FA and two other isoprene products, GA and MG. Further, the magnitudes of the nonzero FA intercept exhibited in these correlation plots are found to qualitatively agree with the fraction of precursors that did not concomitantly produce GA and MG. Inspection of specific flights showed direct evidence of the dominance of isoprene as a precursor for FA, appreciable contribution of FA to CO, and negligible decay of FA overnight. Because of the dominant role isoprene plays as a precursor of FA, FA could be used as a proxy of isoprene for assessing the applicability of various versions of biogenic emission inventory.

Evaluation of GOME satellite measurements of tropospheric NO2 and HCHO using regional data from aircraft campaigns in the southeastern United States

“…The NO 2 distribution is highly skewed with a median that is half of the mean, indicative of direct NO x emissions with high spatial heterogeneity. The HCHO measurements are normally distributed reflecting chemical production from VOC oxidation [Lee et al, 1998;Wert et al, 2003a] and more spatially homogeneous sources.…”

“…HCHO was measured as part of TexAQS using tunable diode laser absorption spectroscopy at 10-s resolution with a total uncertainty better than ±(120 pptv + 10%) prior to 1 September, and at 1-s resolution with a total uncertainty better than ±(400 pptv + 10%) during 1 -13 September [Wert et al, 2003b]. For SOS, a liquid phase derivitization technique was used to measure HCHO [Lee et al, 1998], but instrumental issues resulted in data loss at altitudes above 2000 m, precluding reconstruction of HCHO columns for comparison to GOME for this mission.…”

“…Enhancements of HCHO reflect oxidation of VOC emissions from biogenic [Lee et al, 1998;Palmer et al, 2003] and anthropogenic [Wert et al, 2003a] sources. We use GOME observations of HCHO columns to examine the regional scale and temporal variation of VOC emissions over eastern Texas.…”

Design and performance of a tunable diode laser absorption spectrometer for airborne formaldehyde measurements

“…In many cases the important CH 2 O precursors also contribute substantially to total atmospheric hydroxyl radical (OH) hydrocarbon reactivity. As a result, measurements of CH 2 O provide a valuable check of photochemical model predictions concerning recent hydrocarbon oxidation [Liu et al, 1992;Lee et al, 1998;Fried et al, 2002Fried et al, , 2003aWert et al, 2003]. In addition, CH 2 O measurements are important to the calculation of accurate OH concentration fields and odd hydrogen (HO x ) budgets [Ayers et al, 1997;Fried et al, 1997a;Wennberg et al, 1998;Jaeglé et al, 2000].…”

“…Only a small number of VOCs are both abundant and efficient CH 2 O producers, however. These important CH 2 O precursors are methane in the background atmosphere [Finlayson-Pitts and Pitts, 1986;Heikes, 1992;Greenberg et al, 1992], and the terminal alkenes in polluted regimes [Dodge, 1990;Lee et al, 1998;Goldan et al, 2000;Wert et al, 2003]. In many cases the important CH 2 O precursors also contribute substantially to total atmospheric hydroxyl radical (OH) hydrocarbon reactivity.…”