The roles of hydroxyl and hydroperoxyl radical in urban and regional pollution: results from recent measurements

All pollution is local, but the effects can be global. Atmospheric oxidation chemistry converts local chemical emissions into the important secondary pollutants ozone and aerosols. The conversion process is driven in large part by the hydroxyl and hydroperoxyl radicals, together called HOx (HOx = OH + HO2). In the last decade, several tropospheric field studies have included HOx measurements in an attempt to test the understanding of atmospheric oxidation chemistry. The first ground-based field studies that included OH measurements suggested that measured OH was less than modeled OH. Speculation was that chemicals that react with OH were not included in the models. As the number of field studies and HOx measurements has expanded, the picture has gotten much more complicated. Now, studies show that measured HOx can be less than, equal to, or greater than expected, depending on the location and the other pollutants. We examine the current status of results from HOx measurements in the lower troposphere and present some conclusions.