Yongjing Zhao

Atmospheric hydrogen cyanide (HCN) : Biomass burning source, ocean sink?

The observed seasonal amplitude of atmospheric HCN concentrations implies an atmospheric lifetime of only a few months for HCN, much shorter than is commonly assumed from oxidation by OH (a few years). We propose that ocean uptake provides the missing sink, and show with a global 3-D model simulation that the observations of atmospheric HCN can be roughly reproduced in a scenario where biomass burning provides the main source (1.4–2.9 Tg N yr−1) and ocean uptake provides the main sink (HCN atmospheric lifetime of 2–4 months). Such a budget implies that HCN is a sensitive tracer of biomass burning on large scales, of particular value because it is readily observed from space. The ocean sink hypothesis can be tested with measurements of HCN concentrations in marine air and seawater.

An assessment of aircraft as a source of particles to the upper troposphere

Condensation nuclei measurements are examined in conjunction with measurements of reactive nitrogen species (NOy) to identify aircraft plumes in primary air traffic corridors over the North Atlantic. Several hundred plumes exhibiting ≥100 pptv enhancements in NOy mixing ratio were observed. The plumes were typically a few hundred meters wide, exhibited high NO/NOy ratios, and ranged in age from ∼10 minutes to ∼10 hours. Assuming the sampled aircraft emitted ∼12 g NOx (as NO2) kg−1 fuel burned and that the loss of NOy to the particle phase was negligible, we calculate median aerosol emission indices in terms of number of particles kg−1 of fuel burned of ∼120×1015 for CN ≥8 nm in size; ∼50×1015 for CN ≥ 17 nm; and ∼3×1015 for the nonvolatile CN ≥ 17 nm. Using published fuel burn statistics, background aerosol concentrations, and a 10 day particle lifetime, we conclude that present aviation sources enhance global averaged upper-tropospheric fine and nonvolatile aerosol number densities by ∼6% and ∼3%, respectively.

Accuracy of total ozone column amounts observed with solar infrared spectroscopy

Total ozone column amounts were observed at Rikubetsu (43.5°N, 143.8°E), Japan on 90 days between May 18, 1995 and April 26, 1996 with a high-resolution infrared (IR) Fourier transform spectrometer and compared with Dobson spectrometer measurements. The sensitivities of the analysis for IR solar absorption spectra to initial profiles were examined using two kinds of initial profiles for ozone and temperature, namely monthly and yearly averages. IR/Dobson mean column ratios in the two cases were 1.02 and 1.03 and the standard deviation of the ratios were 3.7 and 4.1%, which correspond to 14 and 16 Dobson Units. The standard deviations are smaller than or comparable to the amplitudes of the day-to-day total ozone column variations indicating that day-to-day variations can be detected using monthly or yearly averaged profiles. However, significant solar zenith angle (SZA) dependences were observed in the columns derived using yearly averaged profiles. The SZA dependence was most significant in January and February when the ozone amount in the lower stratosphere was largest. The SZA dependence is considered to be caused by the difference between initial and actual ozone profiles.

Wintertime stratospheric ozone changes over Japan since 1991

Total ozone and ozonesonde data obtained in Sapporo (43°N), Tsukuba (36°N), Kagoshima (32°N), and Naha (26°N) since 1991 were analyzed to study the stratospheric ozone changes over Japan. It was found that sizable total ozone anomalies occurred in the winters of 1992/93 and 1994/95 at the four stations, although the duration and magnitude of the ozone decreases were different between the two periods. Ozone profiles showed increases in ozone concentration above 26 km in the winter of 1991/92 and the most pronounced ozone depletion in the winter of 1992/93 at the four stations. The altitude regions of significant ozone losses in Sapporo, Tsukuba, and Kagoshima in the winter of 1994/95 were higher than those in 1992/93. The latitudinal differences in the degree of ozone losses between 26°N and 43°N since 1991 are presented. The effects of the volcanic aerosol from the Pinatubo eruption and Quasi Biennial Oscillation (QBO) on total ozone are discussed.