Regional Relationship between CO and O3 in New England

The seasonality and interannual variability in the mixing ratios of ozone (O₃) and carbon monoxide (CO) and their inter-relationship were investigated at the rural low elevation site Thompson Farm (TF) and the hill site Castle Springs (400 m above ground level) in southern New Hampshire using continuous observations (2001-2003) from the Atmospheric Investigation, Regional Modeling, Analysis and Prediction (AIRMAP) program at University of New Hampshire (UNH). Our results show distinct site-dependent characteristics in temporal variations on various time scales in O₃ and CO and particularly large interannual variability in fall and winter at both sites. The grouped O₃ and CO data, based on wind speed and direction over different time periods of the day, showed largely varying probability distribution functions (PDF). It was found that only 10% of the seasonal observations formed a positive O₃-CO linear correlation, leading to an estimate of 370 M moles d^-1 for O₃ export from the northeastern U.S. This estimate is three times smaller than previous studies. We used a ratio analysis (NO/NO_y and NO_y/CO) to show that the linear O₃-CO relationships were a result of multiple processes rather than simply either photochemical or depositonal loss processes as proposed by previous work. One of the most important features of the O₃-CO relationship is the lower CO boundary, for which we attempeted to provide physical and chemical interpretations.