Photochemistry of nitrogen oxides and ozone on urban, regional, and global scales

Chemical reactions of nitrogen oxides (NOy) in the troposphere govern the rate of ozone production, the chain length of the odd hydrogen catalytic cycle, and the extent to which anthropogenic emissions influence nearby ecosystems. The unique capabilities of the thermal dissociation laser induced fluorescence (TD-LIF) technique permit the acquisition of accurate and precise measurements of the dominant forms of tropospheric nitrogen oxides, with high resolution in time and space. In Chapter 2 of this dissertation, nitrogen oxides are examined on the global scale using aircraft measurements of total peroxynitrates, the dominant form of nitrogen oxides in the high-latitude spring troposphere. Measurements of HO2NO 2 and CH3O2NO2 agreed to better than 35% with a model that includes the overtone infrared photolysis of peroxynitric acid (J=1x10-5 s-1) at temperatures below 240 K, where we calculate HO2NO2 is about 20 % of total NOy. Under these conditions, the reaction of OH with HO2NO 2 is estimated to account for as much as one third of the permanent loss of hydrogen radicals.; Chapters 3 through 6 utilize measurements of speciated nitrogen oxide compounds, ozone, and other correlative variables from three sites in Central California located along the dominant flow vector between Sacramento and Lake Tahoe. An annual cycle of speciated NOy measurements obtained at the high elevation surface site allows us to investigate the diurnal and seasonal cycles of nitrogen oxides at a location influenced by both the polluted boundary layer and the free troposphere (Chapter 3). In Chapter 4, I combine measurements from UC Berkeley research sites with data from routine monitoring sites in urban Sacramento and downwind locations to examine the influence of human activity patterns on the concentrations of ozone and its precursors. This analysis is developed in Chapter 5 by using day of week patterns in odd oxygen, VOC and NOy to quantify the relative roles of local production and transport in ozone accumulation rates. A Lagrangian analysis, constrained by our observations in the western Sierra Nevada, shows that the direct effect of nitrogen oxides in the Sacramento urban plume on air and water quality in the Lake Tahoe Basin is negligible.