Sources and sinks of formic, acetic, and pyruvic acids over central Amazonia: 2. Wet season

摘要: We have determined the gas phase concentrations of formic (HCOOH), acetic (CH3COOH), and pyruvic (CH3C(O)COOH) acids in forest canopy, boundary layer, free troposphere over central Amazon Basin during April–May segment 1987 wet season. At 150-m altitude layer daytime average were 430±225, 340±155, 25± 5 ppt for HCOOH, CH3COOH, CH3C(O)COOH, respectively. These values fivefold lower than those observed 1985 dry Concentrations measured near canopy top not significantly different from (P = 0.10), while less. (5 km) averaged 170±40, 210±40, 15±15 Fivefold enhancements CH3C(O)COOH convective outflows at 5- to 6-km altitudes. Aerosol carboxylate usually below our detection limit 5–10 ppt. Preliminary branch enclosure measurements indicated significant direct emission carboxylic by vegetation. A one-dimensional photochemical model was used examine contributions various sources acid budgets. Model results indicate that emissions vegetation can account most canopy. peak hours, 24-hour upward fluxes are 4.4×109, 3.7×109, 2.8×108 molecules cm−2 s−1 However, only a small fraction suggesting large contribution atmospheric sources. The reactions previously suggested literature as (gas decomposition isoprene, CH3CO3 + peroxy, aqueous oxidation CH2O) appear be too slow explain concentrations. Other reactions, so far unidentified, could make major