43 research outputs found
Highly functionalized organic nitrates in the southeast United States : Contribution to secondary organic aerosol and reactive nitrogen budgets
Speciated particle-phase organic nitrates (pONs) were quantified using online chemical ionization MS during June and July of 2013 in rural Alabama as part of the Southern Oxidant and Aerosol Study. A large fraction of pONs is highly functionalized, possessing between six and eight oxygen atoms within each carbon number group, and is not the common first generation alkyl nitrates previously reported. Using calibrations for isoprene hydroxynitrates and the measured molecular compositions, we estimate that pONs account for 3% and 8% of total submicrometer organic aerosol mass, on average, during the day and night, respectively. Each of the isoprene-and monoterpenes-derived groups exhibited a strong diel trend consistent with the emission patterns of likely biogenic hydrocarbon precursors. An observationally constrained diel box model can replicate the observed pON assuming that pONs (i) are produced in the gas phase and rapidly establish gas-particle equilibrium and (ii) have a short particle-phase lifetime (similar to 2-4 h). Such dynamic behavior has significant implications for the production and phase partitioning of pONs, organic aerosol mass, and reactive nitrogen speciation in a forested environment.Peer reviewe
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Observation of isoprene hydroxynitrates in the southeastern United States and implications for the fate of NO<sub><i>x</i></sub>
Isoprene hydroxynitrates (IN) are tracers of the photochemical oxidation of
isoprene in high NO<sub><i>x</i></sub> environments. Production and loss of IN have a
significant influence on the NO<sub><i>x</i></sub> cycle and tropospheric O<sub>3</sub>
chemistry. To better understand IN chemistry, a series of photochemical
reaction chamber experiments was conducted to determine the IN yield from
isoprene photooxidation at high NO concentrations (> 100 ppt). By
combining experimental data and calculated isomer distributions, a total IN
yield of 9(+4/−3) % was derived. The result was applied in a
zero-dimensional model to simulate production and loss of ambient IN
observed in a temperate forest atmosphere, during the Southern Oxidant and
Aerosol Study (SOAS) field campaign, from 27 May to 11 July 2013. The 9 %
yield was consistent with the observed IN/(MVK+MACR) ratios observed
during SOAS. By comparing field observations with model simulations, we
identified NO as the limiting factor for ambient IN production during SOAS,
but vertical mixing at dawn might also contribute (~ 27 %)
to IN dynamics. A close examination of isoprene's oxidation products
indicates that its oxidation transitioned from a high-NO dominant chemical
regime in the morning into a low-NO dominant regime in the afternoon. A
significant amount of IN produced in the morning high NO regime could be
oxidized in the low NO regime, and a possible reaction scheme was proposed