Effect of NO<sub>x</sub> level on secondary organic aerosol (SOA) formation from the photooxidation of terpenes

Abstract

Abstract. Secondary organic aerosol (SOA) formation from the photooxidation of one monoterpene (α-pinene) and two sesquiterpenes (longifolene and aromadendrene) is investigated in the Caltech environmental chambers. The effect of NO x on SOA formation for these biogenic hydrocarbons is evaluated by performing photooxidation experiments under varying NO x conditions. The NO x dependence of α-pinene SOA formation follows the same trend as that observed previously for a number of SOA precursors, including isoprene, in which SOA yield (defined as the ratio of the mass of organic aerosol formed to the mass of parent hydrocarbon reacted) decreases as NO x level increases. The NO x dependence of SOA yield for the sesquiterpenes, longifolene and aromadendrene, however, differs from that determined for isoprene and α-pinene; the aerosol yield under high-NO x conditions substantially exceeds that under low-NO x conditions. The reversal of the NO x dependence of SOA formation for the sesquiterpenes is consistent with formation of relatively low-volatility organic nitrates, and/or the isomerization of large alkoxy radicals leading to less volatile products. Analysis of the aerosol chemical composition for longifolene confirms the presence of organic nitrates under high-NO x conditions. Consequently the formation of SOA from certain biogenic hydrocarbons such as sesquiterpenes (and possibly large anthropogenic hydrocarbons as well) may be more efficient in polluted air.

Real Time In Situ Detection of Organic Nitrates in Atmospheric Aerosols

“…Total particle mass was calculated from the SMPS data assuming a particle density of 1.2 g cm −3 which is similar to that reported in a number of studies for high-NO x SOA of terpenes (39)(40)(41)(42)(43)(44). Particle number distributions were typically centered at 100 -150 nm.…”

Secondary organic aerosol (SOA) formation from reaction of isoprene with nitrate radicals (NO<sub>3</sub>)

“…Typically, we scan from m/z 50 to 400. More details about the CIMS technique are given in Crounse et al (2006) and Ng et al (2007a). Because authentic standards are not available for the major products, sensitivities are not experimentally determined.…”

Development of a sensitive long path absorption photometer to quantify peroxides in aerosol particles (Peroxide-LOPAP)

“…SOA was produced from α-pinene as biogenic precursor. The experiments were done at 20 • C. A scanning mobility particle sizer (SMPS, consisting of a differential mobility analyser (DMA, TSI 3071) and a condensation particle counter (CPC, TSI 3022)) measured the particle size distribution, which was converted to a mass concentration assuming spherical particle geometry with a density of 1.3 g cm −3 (Alfarra et al, 2006;Ng et al, 2007). O 3 , NO, and NO 2 were all continuously monitored.…”