Effect of the nitrate group on yields and composition of secondary organic aerosol formed from reactions of alkyl nitrates with OH radicals in the presence of NOx
A systematic study was conducted on the effect of a nitrate functional group on secondary organic aerosol (SOA) products and yields from reactions of C10 alkyl nitrate isomers with OH radicals in the presence of NOx. The 1- through 5-decyl nitrate isomers were synthesized from their corresponding alcohols, reacted in an environmental chamber, and the precursors and SOA were analyzed using online and offline techniques. SOA products were analogous to those formed from similar reactions of the C10 n-alkane (decane), but with an additional nitrate group. The SOA yield was highest when the nitrate group was on the terminal carbon and decreased monotonically from 0.51 to 0.50, 0.44, 0.28, and 0.15 as it moved toward the center of the molecule, at which point it was similar to that from decane. The explanation for this trend, which is supported by results of calculations performed using a kinetics model, involves a combination of the effects of the nitrate group on product vapor pressures and reaction branching ratios. In general, although the nitrate group lowers the vapor pressures of products relative to the corresponding products of the decane reaction, thus enhancing gas-to-particle partitioning and SOA formation, as it moves toward the center of the molecule it also alters the branching ratios for reaction pathways so as to enhance the formation of more volatile products. The results are compared with those from similar studies on ketone and alcohol isomers to gain a more comprehensive understanding of the effects of functional groups on SOA composition and yields.
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