HOx chemistry during INTEX-A 2004: Observation, model calculation, and comparison with previous studies

This mission, which was conducted mainly over North America and the western Atlantic Ocean in summer 2004, was an excellent test of atmospheric oxidation chemistry. The HOx results from INTEX-A are compared to those from previous campaigns and to results for other related measurements from INTEX-A. Throughout the troposphere, observed OH was generally 0.95 of modeled OH; below 8 km, observed HO₂ was generally 1.20 of modeled HO₂.

This observed-to-modeled comparison is similar to that for TRACE-P, another midlatitude study for which the median observed-to-modeled ratio was 1.08 for OH and 1.34 for HO₂, and to that for PEM-TB, a tropical study for which the median observed-to-modeled ratio was 1.17 for OH and 0.97 for HO₂. HO₂ behavior above 8 km was markedly different. The observed-to-modeled HO₂ ratio increased from ~1.2 at 8 km to ~3 at 11 km with the observed-to-modeled ratio correlating with NO. Above 8 km, the observed-to-modeled HO₂ and observed NO were both considerably greater than observations from previous campaigns.