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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 find that the column ozone and EDD has a similar to 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.

Plain Language Summary Anomalously high surface ultraviolet (UV) radiation is present over southwest United States during the July-August North American monsoon. This elevated radiation results from the lifting of the tropopause and subsequent reduction of the ozone column. Simultaneously, water vapor in the upper troposphere and lower stratosphere (UTLS) increases as a result of the monsoon convection. Thus, summer monsoon increases in UV radiation and the erythemal daily dosage are correlated with enhanced UTLS water vapor, but this correlation does not appear to be a signal of unusual stratospheric chemical ozone loss.