Observations of the temperature dependent response of ozone to NOx reductions in the Sacramento, CA urban plume

摘要

Observations of NO in the Sacramento, CA region show that mixingratios decreased by 30 % between 2001 and 2008. Here we use anobservation-based method to quantify net ozone (O) production rates in theoutflow from the Sacramento metropolitan region and examine the Odecrease resulting from reductions in NO emissions. This observationalmethod does not rely on assumptions about detailed chemistry of ozoneproduction, rather it is an independent means to verify and test theseassumptions. We use an instantaneous steady-state model as well as adetailed 1-D plume model to aid in interpretation of the ozone productioninferred from observations. In agreement with the models, the observationsshow that early in the plume, the NO dependence for O(O = O + NO) production is strongly coupled with temperature,suggesting that temperature-dependent biogenic VOC emissions and othertemperature-related effects can drive O production betweenNO-limited and NO-suppressed regimes. As a result, NOreductions were found to be most effective at higher temperatures over the 7year period. We show that violations of the California 1-h Ostandard (90 ppb) in the region have been decreasing linearly with decreasesin NO (at a given temperature) and predict that reductions of NOconcentrations (and presumably emissions) by an additional 30 % (relativeto 2007 levels) will eliminate violations of the state 1 h standard inthe region. If current trends continue, a 30 % decrease in NO isexpected by 2012, and an end to violations of the 1 h standard in theSacramento region appears to be imminent.