Observations of Tropospheric Trace-Gases and Techniques for Assessing the Regional Transport of Air-Pollutants

Two techniques were used to assess regional transport of gaseous air pollutants. The first involved conducting airborne measurements of vertical profiles of the trace gases CO, O_3, and reactive nitrogen compounds near convective clouds, followed by analysis and interpretation with detailed meteorological data. The second technique involved applying spectral and cross spectral analyses to surface-based time series of simultaneous trace gas concentrations and wind data. Airborne measurements were conducted near a line of deep convective clouds in south-central Oklahoma. Trace gas concentrations in the upper tropospheric outflow region of these clouds were near levels found in the surrounding environment. Meteorological analyses showed that these clouds were located above a cold front, which prevented the entry of air from the boundary layer directly below the cloud. These results suggest that the large amount of vertical trace gas transport noted in previous observations and model results cannot simply be extrapolated to all convective cells. Another flight was conducted during clear-sky conditions over north-central Oklahoma and central Kansas. Correlation analyses were conducted on vertical profiles of pairs of trace gases to infer the sources of these gases. Areas of ozone predominantly produced photochemically in the troposphere and areas with ozone of primarily stratospheric origin were identified. Elevated CO and reactive nitrogen compound concentrations found in the upper troposphere were carried by convective clouds from the boundary layer to the upper troposphere in a polluted region 600 km upstream from the measurement location. Spectral analysis of trace gas concentration time series and cross spectral analysis of concentration and wind component series were used to identify the chemical and physical processes affecting the concentrations and to determine the scales of atmospheric motion that are most important in the flux of the gases. Flux vectors for certain spatial wavelengths were related to known emission patterns. The majority of the fluxes of SO_2 at a site near Chicago and of reactive nitrogen compounds at both this site and at Boulder, Colorado were associated with synoptic-scale atmospheric motions and concentration gradients. Regression coefficient spectra showed the influence of smaller-scale wind fluctuations on concentrations.