Measurement of the Photodissociation Coefficient of NO2 in the Atmosphere: II. Stratospheric Measurements

The photodissociation coefficient of NO2, J NO 2, has been measured from a balloon platform in the stratosphere. Results from two balloon flights are reported. High Sun values of J NO 2 measured were 10.5±0.3 and 10.3±0.3×10-3 s-1 at 24 and 32 km respectively. The decrease in J NO 2 at sunset was monitored in both flights. The measurements are found to be in good agreement with calculations of J NO 2 using a simplified isotropic multiple scattering computer routine

The distribution of nitrogen oxides off the East Coast of North America

Measurements of NO and NOx' (as measured by a chemiluminescent analyzer equipped with a FeSO4 converter) were made from an aircraft off the east coast of North America in January and February 1986. These measurements show the mixing ratios of the nitrogen oxides to be higher than encountered in remote continental or marine environments. Both the free troposphere and boundary layer mixing ratio distributions are skewed to ward high mixing ratios and are best described by a gamma probability distribution. The mean mixing ratios observed were 2.9 parts per billion by volume (ppbv) in the boundary layer and 0.55 ppbv in the free troposphere for NOx', and 0.56 ppbv in the boundary layer and 0.18 in the free troposphere for NO

Nitrogen and sulphur over the Western Atlantic Ocean

This paper reports new surface and aircraft measurements of sulphur and nitrogen species made during WATOX-85 at Lewes, Delaware and Bermuda. Concentrations of most species measured in this portion of the western Atlantic Ocean atmosphere were higher than those found in remote marine environments, showing clearly the influence of anthropogenic emissions from North America. The experiment was designed such that measurements were made following cold frontal passages in conditions of strong, dry westerly flow, to ensure that measurements at Bermuda were in air masses that had earlier crossed the east coast in the region of Lewes. Boundary-layer SO2 concentrations decreased by a factor of 20 between the east coast and Bermuda, while sulphate was the same at both locations. First-order decay distances for SO2 and total S were 340 and 620 km, respectively, under these conditions. The decay distance for total S is substantially shorter than previously determined, indicating that SO2 in particular is removed in near-coastal environments more quickly than previously supposed. Boundary-layer NOx and HNO3 concentrations decreased by close to an order of magnitude between the east coast and Bermuda, whereas for NO3− the decrease was a factor of two. Corresponding first-order decay distances of NO'x and total N were 500 and 550km, respectively

Description and Intercomparison of Techniques to measure N and S compounds in the Western Atlantic Ocean Experiment

The data set of N and S compound measurements from WATOX-85 has been examined in detail to assess that data quality and suitability for use in addressing the goals of the Western Atlantic Ocean Experiment. Accuracy estimates for particulate SO42− and NO3−, SO2 and HNO3 have been made on the basis of the investigators' estimates and the results of intercomparisons. Intercomparisons of ground-based particulate SO42− and all filter SO2 and HNO3 measurements show them to be consistent with the 20% accuracies quoted by the investigators. Ground-based particulate NO3− and aircraft particulate SO42− show inconsistencies such that the accuracies can be no better than 28% and the aircraft particulate NO3 has an accuracy of no better than 60%

The Reactions of Ozone with Methyl and Ethyl Nitrites

The reactions of O3 with CH3ONO and C2H5ONO were studied using infrared absorption spectroscopy in a static reactor at temperatures between 298 and 352

The Influence of the Nocturnal Boundary Layer on Secondary Trace Species in the Atmosphere at Dorset, Ontario

The impact of the nocturnal boundary layer (NBL) on the concentrations of O3, H2O2, PAN and CH2O has been studied for two 4-day periods, one in the summer of 1989 and the other in the spring of 1990. Where the presence of the nocturnal layer is clear, O3, PAN and CH2O concentrations decrease rapidly and these species appear to be deposited to the surface. Break-up of the inversion in the morning returns concentrations to levels typical of the previous day. H2O2 is removed much faster than the other species and it is replenished much more slowly. This appears to be due to the H2O2 dissolving in water droplets resulting from the rapid cooling of the air. There is evidence for a morning maximum in PAN, likely due to the combination of high concentrations being brought downwards during the break-up of the NBL followed by thermal decomposition

Measurement of the Photodissociation Coefficient of NO2 in the Atmosphere: I. Method and Surface Measurements

The photodissociation coefficient of NO2, J NO 2, has been measured from a balloon platform in the stratosphere. Results from two balloon flights are reported. High Sun values of J NO 2 measured were 10.5±0.3 and 10.3±0.3×10-3 s-1 at 24 and 32 km respectively. The decrease in J NO 2 at sunset was monitored in both flights. The measurements are found to be in good agreement with calculations of J NO 2 using a simplified isotropic multiple scattering computer routine

Calculations of the Temperature Dependence of the NO2 Photodissociation Coefficient in the Atmosphere

The photodissociation coefficient, J NO2 of NO2 in the atmosphere was calculated at 235 and 298 K using the measured temperature dependences of the absorption cross-sections and quantum yields. These calculations gave a ratio J NO2(298 K)/J NO2(235 K)=1.155±0.010 which is only weakly dependent on altitude, surface albedo and solar zenith angle

Relationships between PAN, PPN, O3 and NOx at Urban and Rural sites in Ontario

PAN concentrations were determined during the summer of 1989 and the winter of 1990 at three sites in Ontario representing urban (Toronto), suburban downwind (Stouffville) and rural (Dorset) locations. PAN concentrations were found to reach levels of ≈ 4 ppb in Toronto under conditions of stagnant southerly air flow. Observed PAN concentrations were compared with concurrent measurements of PPN and O3. PPN concentrations were found to be, on average, between 8 and 11% of those of PAN, with slightly higher PPN/PAN ratios found for air masses that were relatively anthropogenic-pollution impacted. For the Dorset site, however, the dependence on air-mass origin was small. The slopes of regressions of ozone vs PAN were found to increase substantially from urban to rural air masses, with typical O3/PAN ratios for a mid-range ozone concentration of 50 ppb being 50, 110 and 330, for Toronto, Stouffville and Dorset, respectively. Analysis of the data for Toronto and Stouffville under varying meteorological conditions indicates significant potential for oxidant production in the absence of transport of pollutants from other sources