Chemical kinetics and photochemical data for use in stratospheric modeling

Rate constants and photochemical cross sections are presented. The primary application of the data is for modeling of the stratospheric processes, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena

Chemical kinetic and photochemical data for use in stratospheric modelling

An evaluated set of rate constants and photochemical cross sections were compiled for use in modelling stratospheric processes. The data are primarily relevant to the ozone layer, and its possible perturbation by anthropogenic activities. The evaluation is current to, approximately, January, 1979

Kinetic studies of nitrate radicals: flash photolysis at 193 nm

Nitrate radicals, NO3, were produced for the first time by 193 nm laser flash photolysis of N2O5 and HNO3. Detection was achieved due to NO3’s strong absorption at 622.7 nm confirmed by measurements of the absorption spectrum in the range of 617 to 625 nm using both NO3 precursors. Time-resolved kinetic studies allowed the determination of room temperature rate coefficients for the reactions of NO3 with 2-methylbut-2-ene and NO2 of (1.28 ± 0.11) × 10−11 and (8.4 ± 1.2) × 10−13 cm3 molecule−1 s−1, respectively. The rate coefficients compare well to previous measurements with alternative techniques suggesting that the reported method is valid and may be applied in follow-up studies. The rate coefficient for 2-methylbut-2-ene is compared to previous measurements and predictions for the alkene as well as the related alkenol. The new data confirm a previously suggested deactivation of the reactive site of the double bond if adjacent to an OH group. A calculated atmospheric lifetime for 2-methylbut-2-ene with respect to NO3-initated oxidation of less than 3 min suggests predominant removal by NO3 in the atmosphere

Evolution of HCl Concentrations in the Lower Stratosphere from 1991 to 1996 Following the Eruption of Mt. Pinatubo

Geophysical Research Letters, Vol. 25, No. 7, pp. 995-998, April 1, 1998.In situ measurements of hydrochloric acid in the lower stratosphere reveal that its mean abundance relative to that of total inorganic chlorine..

Tropical entrainment time scales inferred from stratospheric N_2O and CH_4 observations

Simultaneous in situ measurements of N_2O and CH_4 were made with a tunable diode laser spectrometer (ALIAS II) aboard the Observations from the Middle Stratosphere (OMS) balloon platform from New Mexico, Alaska, and Brazil during 1996 and 1997. We find different compact relationships of CH_4 with N_2O in the tropics and extra-tropics because mixing is slow between these regions. Transport into the extra-tropics from the tropics or the polar vortex leads to deviations from the normal compact relationship. We use measured N_2O and CH_4 and a simple model to quantify entrainment of mid-latitude stratospheric air into the tropics. The entrainment time scale is estimated to be 16 (+17, −8) months for altitudes between 20 and 28 km. The fraction of tropical air entrained from the extra-tropical stratosphere is 50% (+18%, −30%) at 20 km, increasing to 78% (+11%, −19%) at 28 km

The response of ClO radical concentrations to variations in NO_2 radical concentrations in the lower stratosphere

The response of ClO concentrations to changes in NO_2 concentrations has been inferred from simultaneous observations of [ClO], [NO], [NO_2] and [O_3] in the mid-latitude lower stratosphere. This analysis demonstrates that [ClO] is inversely correlated with [NO_2], consistent with formation and photolysis of [ClONO_2]. A factor of ten range in the concentration of NO_2 was sampled (0.1 to 1×10^9 mol/cm^3), with a comparable range in the ratio of [ClO] to total available inorganic chlorine (1% ≤ [ClO]/[Cl_y] ≤ 5%). This analysis leads to an estimate of [ClONO_2]/[Cl_y] = 0.12 (×/÷2), in the mid-latitude, lower-stratospheric air masses sampled

Ozone destruction and production rates between spring and autumn in the Arctic stratosphere

In situ measurements of radical and long-lived species were made in the lower Arctic stratosphere (18 to 20 km) between spring and early autumn in 1997. The measurements include O_3, ClO, OH, HO_2, NO, NO_2, N_(2)O, CO, and overhead O_3. A photochemical box model constrained by these and other observations is used to compute the diurnally averaged destruction and production rates of O3 in this region. The rates show a strong dependence on solar exposure and ambient O_3. Total destruction rates, which reach 19%/month in summer, reveal the predominant role of NO_x and HO_x catalytic cycles throughout the period. Production of O_3 is significant only in midsummer air parcels. A comparison of observed O_3 changes with destruction rates and transport effects indicates the predominant role of destruction in spring and an increased role of transport by early autumn

NO(y) partitioning from measurements of nitrogen and hydrogen radicals in the upper troposphere

Recent studies using NO, NO(y), OH and HO2 (HO(X)) observations have postulated acetone and convection of peroxides as significant sources of HO(X) in the upper troposphere (UT). This work focuses on the effect these additional HO(X) sources have on the modeled NO(y) partitioning and comparisons of the modeled NO(x)/NO(y) ratio to observations. The measured NO(x)/NO(y) ratio is usually much higher than predicted regardless of the presence of acetone in the model. The exception occurs for air parcels having low NO(y) and O3 values. For these air parcels the measured NO(x)/NO(y) ratio is much lower than the calculated ratio unless acetone is included in the model. In all cases acetone increases the fraction of NO(y) that is peroxy acetyl nitrate (PAN) from typical values of much less than 0.1 to values as high as 0.35. Including acetone also reduces the scatter in a comparison between modeled and observed NO(x)/NO(y) ratios

Comparison of modeled and observed values of NO_2 and JNO_2 during the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) mission

Stratospheric measurements of NO, NO_(2), O_(3), ClO, and HO_(2) were made during spring, early summer, and late summer in the Arctic region during 1997 as part of the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) field campaign. In the sunlit atmosphere, NO_(2) and NO are in steady state through NO2 photolysis and reactions involving O_(3), ClO, BrO, and HO_(2). By combining observations of O_(3), ClO, and HO_(2), observed and modeled values of the NO_(2) photolysis rate coefficient (JNO_(2)), and model estimates of BrO, several comparisons are made between steady state and measured values of both NO_(2) and JNO_(2). An apparent seasonal dependence in discrepancies between calculated and measured values was found; however, a source for this dependence could not be identified. Overall, the mean linear fits in the various comparisons show agreement within 19%, well within the combined uncertainties (±50 to 70%). These results suggest that photochemistry controlling the NO_(2)/NO abundance ratio is well represented throughout much of the sunlit lower stratosphere. A reduction in the uncertainty of laboratory determinations of the rate coefficient of NO + O_(3) → NO_(2) + O_(2) would aid future analyses of these or similar atmospheric observations