OH and HO2 concentrations, sources, and loss rates during the Southern Oxidants Study in Nashville, Tennessee, summer 1999 (original) (raw)

2003, Journal of Geophysical Research: Atmospheres

OH and HO2 mixing ratios and total OH reactivity were measured together with photolysis frequencies, NOx, O3, many VOCs, and other trace gases during the midsummer 1999 SOS campaign in Nashville, Tennessee. These measurements provided an excellent opportunity to study OH and HO2 (collectively called HOx), and their sources and sinks in a polluted metropolitan environment. HOx generally showed the expected diurnal evolution, with maxima around noon of up to about 0.8 pptv of OH and 80 pptv of HO2 during sunny days. Overall, daytime observed OH and HO2 were a factor of 1.33 and 1.56 times modeled values, within the combined 2σ instrument and model uncertainties. The chain length of HOx, which is determined from the ratio of the measured total OH reactivity that cycles OH to the total HOx loss, was on average 3–8 during daytime and up to 3 during nighttime, in general agreement with expectations. However, differences occurred between observed HOx behavior and expectations from theory a...