Uptake of carbonyls to atmospheric particulate matter: Ambient measurements and laboratory studies.

摘要

The contribution of volatile and semi-volatile aldehydes and ketones to particulate matter is not well known. In this study the uptake of carbonyls to particulate matter was investigated in both the ambient atmosphere and in a laboratory setting. A method was developed to measure aldehydes and ketones associated with atmospheric particles, involving collection on filters, followed by extraction and derivatization with 2,4-dinitrophenylhydrazine (2,4-DNPH). The method was optimized for 13 carbonyl compounds of atmospheric importance, with detection limits of 0.009--5.6 ng m-3.; Particulate carbonyl compounds were quantified during recent field studies: SONTAS 2000 and Pacific 2001. Median values during these studies ranged from 0.15--12.9 ng m-3 and 0.01--33.9 ng m -3 respectively and were several orders of magnitude higher than could be accounted for with current partitioning theory. This, together with experiments revealing the insignificance of positive adsorption artifacts, and studies of the extraction and derivatization kinetics, suggested the presence of a heterogeneous uptake mechanism.; Reactive uptake of glyoxal onto particulate matter was also studied in laboratory experiments utilizing a reaction chamber. Inorganic seed particles were utilized, including (NH4)2SO4, (NH 4)2SO4/H2SO4, NaCl and NaNO 3, while varying the relative humidity and acid concentration. The organic composition, was measured in situ with an Aerosol Mass Spectrometer (AMS). Regardless of seed composition, particle growth was rapid and continuous over the course of several hours. Identification of mass fragments greater than the glyoxal monomer suggested that heterogeneous reactions had occurred. In addition, temporal analysis of the mass fragments was consistent with a proposed acid catalyzed mechanism whereby glyoxal is first hydrated followed by self-reaction to form cyclic acetal structures. Specific mass fragments were found that could only arise from sulfate esters, and were not present on the non-sulfur containing seed particles.; Growth rates and reactive uptake coefficients, gamma, were derived by fitting a model of particle growth to the experimental data. Organic growth rates varied from 1.05 x 10-11--23.1 x 10-11 mug particle-1 min -1 in the presence of ∼5 ppb glyoxal. Uptake coefficients (gamma) of glyoxal varied from 8.0 x 10-4--7.3 x 10-3 with a median gamma = 2.9 x 10 -3, observed for (NH4)2SO4 seed aerosols at 55% relative humidity. Increased gamma values were related to increased particle acidity, indicating a mild acid catalysis effect. Uptake coefficients point toward a heterogeneous loss of glyoxal in the atmosphere that is at least as important as gas phase loss mechanisms, including photolysis and reaction with hydroxyl radicals. Glyoxal lifetime due to heterogeneous reactions under typical ambient conditions was estimated to be tau het = 5--287 min. In rural and remote areas, the glyoxal uptake can lead to 5--257 ng m-3 of secondary organic aerosols in 8 hours, consistent with recent ambient measurements.