Effects of biogenic nitrate chemistry on the NO<sub>x</sub> lifetime in remote continental regions

Abstract

Abstract.We present an analysis of the NO x budget in conditions of low NO x (NO x = NO + NO 2 ) and high biogenic volatile organic compound (BVOC) concentrations that are characteristic of most continental boundary layers. Using a steady-state model, we show that below 500 pptv of NO x , the NO x lifetime is extremely sensitive to organic nitrate (RONO 2 ) formation rates. We find that even for RONO 2 formation values that are an order of magnitude smaller than is typical for continental conditions significant reductions in NO x lifetime, and consequently ozone production efficiency, are caused by nitrate forming reactions. Comparison of the steady-state box model to a 3-D chemical transport model (CTM) confirms that the concepts illustrated by the simpler model are a useful approximation of predictions provided by the full CTM. This implies that the regional and global budgets of NO x , OH, and ozone will be sensitive to assumptions regarding organic nitrate chemistry. Changes in the budgets of these species affect the representation of processes important to air quality and climate. Consequently, CTMs must include an accurate representation of organic nitrate chemistry in order to provide accurate assessments of past, present, and future air quality and climate. These findings suggest the need for further experimental constraints on the formation and fate of biogenic RONO 2 .

Mechanism of the hydroxyl radical oxidation of methacryloyl peroxynitrate (MPAN) and its pathway toward secondary organic aerosol formation in the atmosphere

“…In contrast, Lin et al 18 suggest a low HAC yield (B3%). The current work cannot differentiate the 2% of thermalized radical A that is predicted to form, 17 ultimately generating the alkoxyl radical under high NO x conditions, because the products would likely include HAC and NO 3 . Together, the experimental data support the HMML mechanism from the MPAN + OH reaction.…”

“…In high-NO 2 experiments, the added NO 2 and that formed from CH 3 ONO photochemistry conspire to maintain the NO 2 /NO ratio 410 throughout the experiment. Importantly, the near-UV broadband radiation used in this work does not efficiently photolyze NO 3 via mechanisms that yield a net destruction of NO 3 …”

“…Volatile acids and select polar organic compounds were quantified with a custom-built triple-quadrupole chemical ionization mass spectrometer (CIMS, Agilent/Caltech). 26 The CIMS operated in three modes: scanning negative ion mode using CF 3 27 and tandem mass determinations 26 of the CF 3 O À CIMS have been described previously.…”

“…65 We suspect that, in nature, the anionic ring opening polymerization scheme is the active mechanism. Nucleophilic attack at the sp 3 carbon is dominant for a-lactones, 66 partly due to the stability of the carboxylate (estimated to be only B10 kcal mol À1 higher in energy than the a-lactone). 67 The propagated carboxylate can repeatedly add HMML under low RH conditions, where its main fate is reaction with organics that coat the particle.…”

“…This NO x sensitivity translates to regional environmental impacts. For example, the high-NO x oxidation of isoprene controls the production of tropospheric ozone in regions rich with biogenic hydrocarbons [1][2][3] by accelerating the cycling of NO x and producing NO x reservoir species (e.g., organic nitrates and peroxynitrates). Isoprene chemistry also affects global climate primarily through the formation of secondary organic aerosol (SOA).…”