Erythemal Radiation, Column Ozone, and the North American Monsoon

Recently, Anderson et al. (2012, https://doi.org/10.1126/science.1222978, 2017, https://doi.

org/10.1073/pnas.1619318114) and Anderson and Clapp (2018, https://doi.org/10.1039/C7CP08331A)

proposed that summertime convectively injected water vapor over North America could lead to stratospheric

ozone depletion through halogenic catalytic reactions. Such ozone loss would reduce the ozone column and

increase erythemal daily dose (EDD). Using 10 years of observations over the North American monsoon

region from the Aura Ozone Monitoring Instrument, we fi nd that the column ozone and EDD has a ~0.8- 0.9

spatial correlation with lower stratospheric water vapor measured by the Aura Microwave Limb Sounder.

We show that this correlation appears to be due to the elevation of the monsoonal tropopause and associated

monsoonal convection. The increase in tropopause altitude reduces the ozone column and increases EDD.

We see no apparent evidence of substantial heterogeneous chemical ozone loss in lower stratospheric ozone

coincident with the stratospheric monsoonal water vapor enhancement.