Atmospheric oxidation and air pollution in Houston: Lessons from the SHARP 2009 field campaign (Invited)

Predictive skill for urban ozone pollution is thought to be limited primarily by uncertainties in the emissions of pollution precursor gases such as nitrogen oxides and volatile organic compounds and in the meteorology, particularly the boundary layer height and advection. However, point measurements of the hydroxyl radical (OH) and the hydroperoxyl radical (HO2) have shown that uncertainties in the chemical mechanisms are also important. Other measurements, including those of the OH reactivity (i.e., the inverse of the OH lifetime), help constrain the uncertainties. Two new measurements were made for the first time during SHARP. The first was a direct measurement of the ozone production rate. The second was the laser induced fluorescence measurement of OH using two methods - the usual method of alternating the laser wavelength on and off the OH absorption and a second method of periodically adding an OH reactant, akin to the method used by the chemical ionization / mass spectrometry technique. These two new measurements further constrain the uncertainties. We combine these measurements with others and use simple analyses and photochemical box models to examine the oxidation observed during SHARP 2009 and to put it into context of other field campaigns.