Measurement and model results for gas phase OH and H2SO4 during PROPHET 2001.
Abstract
During the summer of 2001 a Chemical Ionization Mass Spectrometer (CIMS) was installed on top of the PROPHET tower to measure OH and H2SO4. Both OH and H2SO4 have a strong diurnal variation and correlate well with the measured ozone photolysis rate. Typical OH nighttime values are below the detection limit of 3e5 molecules cm-3. The maximum daytime value varied from 1-5 e6 molecules cm-3 with the highest OH levels corresponding to the lowest isoprene mixing ratios. The nighttime results are inconsistent with previous LIF measurements of high nighttime OH levels at this site and may indicate a systematic difference between the two techniques. However, the midday measured OH data is approximately 50% higher than the preliminary midday model values and is in accord with the previous LIF observations. A more detailed comparison of constrained photochemical models predictions to the observed OH levels will be presented. The daytime H2SO4 concentrations were highly variable and exceeded 5e7 molecules cm-3 on two days under "clean" northerly flow conditions. Evidence will be presented that suggest the source of the relatively high sulfuric acid concentrations is a large nickel smelting operation in Sudbury, Ontario. The nighttime levels of sulfuric acid were typically below the detection limit of the instrument of approximately 1e5 molecules cm-3. This data is consistent with the measured OH and suggests that large nighttime sources of radicals are not present in this environment.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFM.A51A0037T
- Keywords:
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- 0345 Pollution: urban and regional (0305);
- 0365 Troposphere: composition and chemistry