A re-evaluation of South Pole HOx chemistry based on ISCAT 2000 observations
Abstract
In an earlier study at South Pole (ISCAT 1998 - Investigation of Sulfur Chemistry in Antarctic Troposphere) surprisingly high values of OH were found which were strongly associated with equally unexpected high values of NO. Although this snow released NO was found to explain much of the enhancement in OH, a subset of the total data required still other HOx sources to bring the model predictions into better agreement with the observations. Based on earlier studies at Summit Greenland, these other HOx sources were speculated to consist of snow emissions of CH2O, H2O2, andor HONO, which, unfortunately, were not measured during ISCAT 1998. To be reported here are recent modeling results based on ISCAT 2000 observations of OH and HO2 as well as observations of the HOx precursors: CH2O, H2O2, and HONO. Although it has been suggested that HONO (at lower levels) is the major source of Arctic HOx, we have found that observed South Pole HONO levels are incompatible with both the HOx and NO observations. The model dramatically over-predicts the levels of both HOx and NOx when constrained by observed HONO levels. By contrast, when snow emissions of CH2O and H2O2 are considered, predicted HO2 levels are found to be quite consistent with the limited observations and the agreement with OH is generally within 30%. A budget analysis has revealed that snow emissions of H2 O2 and CH2O are the single most important primary source of South Pole HOx, contributing 46% to the total. Our results suggest that CH2O is about 2 - 3 times more sensitive as a HOx source than H2O2. The major sinks for HOx were shown to be dry deposition of HO2NO2 and HNO3. The relative importance of HNO3 as a sink was found to be highly dependent on the NO level. The higher the NO, the more important was the HNO3 as a HOx sink. Although major progress has been made in improving our understanding of South Pole HOx chemistry based on the ISCAT 2000 study, critical aspects of this chemistry are still in need of further investigation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFM.A12E..03C
- Keywords:
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- 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0322 Constituent sources and sinks;
- 0365 Troposphere: composition and chemistry