Pittsburgh comes in at 11 on NRDC's 'sneeziest and wheeziest' list

PITTSBURGH — The list was created to emphasize the connection between ozone and pollen, and the effect that global warming can have in terms of higher temperature and higher levels of CO2.

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These two factors cause higher levels of pollen and ozone, which can lead to respiratory illness in children and adults.

The ranking for the report goes by the top cities exposed to the combination of the two. Richmond was found to have the most, while Memphis came in second.