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We retrieved column-averaged dry air mole fractions of atmospheric carbon dioxide (X_CO_2) from backscattered short-wave infrared (SWIR) sunlight measured by the Japanese Greenhouse gases Observing SATellite (GOSAT). Over two years of X_CO_2 retrieved from GOSAT is compared with X_CO_2 inferred from collocated SWIR measurements by seven ground-based Total Carbon Column Observing Network (TCCON) stations. The average difference between GOSAT and TCCON X_CO_2 for individual TCCON sites ranges from −0.87 ppm to 0.77 ppm with a mean value of 0.1 ppm and standard deviation of 0.56 ppm. We find an average bias between all GOSAT and TCCON X_CO_2 retrievals of −0.20 ppm with a standard deviation of 2.26 ppm and a correlation coefficient of 0.75. One year of XCO2 was retrieved from GOSAT globally, which was compared to global 3-D GEOS-Chem chemistry transport model calculations. We find that the latitudinal gradient, seasonal cycles, and spatial variability of GOSAT and GEOS-Chem agree well in general with a correlation coefficient of 0.61. Regional differences between GEOS-Chem model calculations and GOSAT observations are typically less than 1 ppm except for the Sahara and central Asia where a mean difference between 2 to 3 ppm is observed, indicating regional biases in the GOSAT X_CO_2 retrievals unobserved by the current TCCON network. Using a bias correction scheme based on linear regression these regional biases are significantly reduced, approaching the required accuracy for surface flux inversions.

The reaction HO_2 + HO_2 → H_2O_2 + O_2(1) has been studied at 100 Torr and 222 K to 295 K. Experiments employing photolysis of Cl_2/CH_3OH/O_2/N_2 and F_2/H_2/O_2/N_2 gas mixtures to produce HO_2 confirmed that methanol enhanced the observed reaction rate. At 100 Torr, zero methanol, k_1 = (8.8 ± 0.9) 10^(−13) × exp[(210 ± 26)/T] cm^3 molecule^(−1) s^(−1) (2σ uncertainties), which agrees with current recommendations at 295 K but is nearly 2 times slower at 231 K. The general expression for k_1, which includes the dependence on bath gas density, is k_1 = (1.5 ± 0.2) × 10^(−12) × exp[(19 ± 31)/T] + 1.7 × 10^(−33) × [M] × exp[1000/T], where the second term is taken from the JPL00-3 recommendation. The revised rate largely accounts for a discrepancy between modeled and measured [H_2O_2] in the lower to middle stratosphere.