Abstract. On April 15 and 19, 1998, two intense dust storms were generated over the Gobi desert by springtime low-pressure systems descending from the northwest. The windblown dust was detected and its evolution followed by its yellow color on SeaWiFS satellite images, routine surface-based monitoring, and through serendipitous observations. The April 15 dust cloud was recirculating, and it was removed by a precipitating weather system over east Asia

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The literature pertinent to reactions of the hydroxyl radical has been reviewed. An extensive discussion is given for reactions of the hydroxyl radical with itself and with CO, H2, and CH4. These four reactions are: (1) OH+OH→H2O+O; (2) CO+OH→CO2+H; (3) H2+OH→H2O+H; (4) CH4+OH→CH3+H2O. Values are recommended for k1 and k2 and for the ratio k3/k2 and k4/k2. These rate ratios are used with the previously established value of k2 to obtain recommended values for k3 and k4. The recommended values in cm3 mol-1·s-1, the temperature range, and the uncertainty are: k1=1.55×1012, 300 K, log k±0.1, 05k2=3.1×1011 exp(−300/T), 300−2000 K, log k±.3k3/k2=73 exp(2300/T), 300−2000 K, log k3/k2±.3k3=3.8×1013 exp(−2600/T), 300−2000 K, log k±.3k4/k2=92 exp(2200/T), 300−2000 K, log k3/k2±.3k4=2.85×1013 exp(−2500/T), 300−2000 K, log k±.7. Rate expressions are also recommended for a number of other hydroxyl reactions whose rates are less well established.

Reactions of the OH radical with OH, H2, and CO have been studied at room temperature in a fast flow system at pressures of the order of 1 mm. The very fast reaction between H atoms and NO2 was used as the source of OH. Electron spin resonance techniques were employed to examine the decay of OH concentration along the flow tube, using NO gas as the calibration standard. Rate constants at 300°K were found to be, in cubic centimeters per mole·second units OH+OH=O+H2O,k2=1.55±0.12×1012,OH+H2=H2O+H,k4=3.9±0.2×109,OH+CO=CO2+H,k5=1.15±0.05×1011. Combination of the last two of these with published results at higher temperatures leads to k4=3.9±0.2×109exp{[(5200±300)/R][(1/300)−(1/T)]},k5=1.15±0.05×1011exp{[(600±300)/R][(1/300)−(1/T)]},or in simple Arrhenius form k4=2.3×1013exp(−5200/RT),k5=3.1×1011exp(−600/RT).

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