NO y partitioning from measurements of nitrogen and hydrogen radicals in the upper troposphere

Recent studies using NO, NO y , OH and HO 2 (HO x ) observations have postulated acetone and convection of peroxides as significant sources of HO x in the upper troposphere (UT). This work focuses on the effect these additional HO x sources have on the modeled NO y partitioning and comparisons of the modeled NO x /NO y ratio to observations. The measured NO x /NO y ratio is usually much higher than predicted regardless of the presence of acetone in the model. The exception occurs for air parcels having low NO y and O 3 values. For these air parcels the measured NO x /NO y ratio is much lower than the calculated ratio unless acetone is included in the model. In all cases acetone increases the fraction of NO y that is peroxy acetyl nitrate (PAN) from typical values of much less than 0.1 to values as high as 0.35. Including acetone also reduces the scatter in a comparison between modeled and observed NO x /NO y ratios.