G. Feingold

Publications (2)4.78 Total impact

• Article: On the Drop-Size Dependence of Organic Acid and Formaldehyde Concentrations in Fog

  B. Ervens, P. Herckes, G. Feingold, T. Lee, J. L. Collett, S. M. Kreidenweis
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  ABSTRACT: Concentration differences between small (r < 8.5="">m) and large droplets(r > 8.5 m) were observed for formic acid, acetic acid and formaldehyde in fog droplets collected in California''s Central Valley. The concentration ratios (large/small droplets) of these compounds were investigated by a stepwise model approach. Assuming thermodynamic equilibrium (KH eff) results in an overestimate of the concentration ratios. Considering the time dependence of gas phase diffusion and interfacial mass transport, it appears that the lifetime of fog droplets might be sufficiently long to enable phase equilibrium for formaldehyde and acetic acid, but not for formic acid (at pH 7). Oxidation by the OH radical has no effect on formaldehyde concentrations but reduces formic acid concentrations uniformly in all drop size classes. The corresponding reaction for acetic acid is less efficient so that only in large droplets, where replenishment is slowed because the uptake rate of acid from the gas phase is slower, is the acid concentration reduced leading to a smaller concentration ratio. Formaldehyde concentrations in fog can be higher than predicted by Henry''s Law due to the formation of hydroxymethanesulfonate. Its formation is dependent on the sulfur(IV) concentration. At high pH values the uptake rate for sulfur(IV) is drop-size dependent. However, the observed concentration ratios for formaldehyde cannot be fully explained by the adduct formation. Finally, it is estimated that mixing effects, i.e., the combination of individual droplets into a bulk sample, have a minor influence (
  Journal of Atmospheric Chemistry 01/2003; 46(3):239-269. · 0.99 Impact Factor
• Article: Secondary organic aerosol yields from cloud-processing of isoprene oxidation products

  B. Ervens, A. G. Carlton, B. J. Turpin, K. E. Altieri, S. M. Kreidenweis, G. Feingold
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  ABSTRACT: While there is a growing understanding from laboratory studies of aqueous phase chemical processes that lead to secondary organic aerosol (SOA) formation in cloud droplets (SOA(drop)), the contribution of aqueous phase chemistry to atmospheric SOA burden is yet unknown. Using a parcel model including a multiphase chemical mechanism, we show that SOA(drop) carbon yields (Y-c) from isoprene (1) depend strongly on the initial volatile organic lcarbon (VOC)/NOx ratio resulting in 42% > Y-c > 0.4% over the atmospherically-relevant range of 0.25 < VOC/NOx < 100; (2) increase with increasing cloud-contact time; (3) are less affected by cloud liquid water content, pH, and droplet number. (4) The uncertainty associated with gas/particle-partitioning of semivolatile organics introduces a relative error of -50% <= Delta Y-c < + 100%. The reported yields can be applied to air quality and climate models as is done with SOA formed on/in concentrated aerosol particles (SOA(aer)).
  Geophysical Research Letters 35(2). · 3.79 Impact Factor