Hydrogen Radicals, Nitrogen Radicals, and the Production of O ₃ in the Upper Troposphere

Abstract

The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HOx required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O3 than expected.

The importance of weak absorption features in promoting tropospheric radical production

“…Studies by Krol et al (6) show a significant global increase in OH, whereas those by Prinn et al (7) show a decline in OH levels after 1988. Recent studies in the upper troposphere also have reported discrepancies between model predictions and measured HO x (where HO X ϵ OH ϩ HO 2 ) concentrations that strongly depend on solar zenith angles (8)(9)(10)(11). These differences between predictions and observation not only highlight the difficulties associated with measuring atmospheric OH concentrations, but also potential variability arising from incomplete accounting of all significant sources and sinks of the OH radical.…”

Design and performance of a tunable diode laser absorption spectrometer for airborne formaldehyde measurements

“…As a result, measurements of CH 2 O provide a valuable check of photochemical model predictions concerning recent hydrocarbon oxidation [Liu et al, 1992;Lee et al, 1998;Fried et al, 2002Fried et al, , 2003aWert et al, 2003]. In addition, CH 2 O measurements are important to the calculation of accurate OH concentration fields and odd hydrogen (HO x ) budgets [Ayers et al, 1997;Fried et al, 1997a;Wennberg et al, 1998;Jaeglé et al, 2000].…”

Distribution and fate of selected oxygenated organic species in the troposphere and lower stratosphere over the Atlantic

“…Oxygenated hydrocarbon species have the potential to play an important role in processes of atmospheric ozone formation [Loyd, 1979;Singh et al, 1995;Wennberg et al, 1998]. Unlike most hydrocarbons, many oxygenated species can be photolyzed throughout the troposphere.…”