Effects of biogenic nitrate chemistry on the NO x lifetime in remote continental regions
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.