Elucidating the relationships between surface-level ozone and meteorology

Surface-level ozone (O3) is associated with respiratory morbidity and mortality, affects vegetation and ecosystems, and impacts the global climate. The cause of day-to-day variations in O3 remains an open question and is key in interpreting past air quality as well as the ways that future climatic changes will affect air pollution. To this end, we investigate the drivers of O3 variability on daily timescales across the Northern Hemisphere with a special emphasis on the United States. Using observations and chemical transport model simulations, we show that positive relationships between O3 and meteorological variables such as temperature and humidity persist only across continental regions in the mid-latitudes (~ 35-60˚N); elsewhere, these relationships are weak or significantly negative. The covariance of O3 with meteorology is driven by an association with transport, not a direct dependence on chemistry or emissions. We find that neither stagnation or cyclones can explain day-to-day variations in O3 or extreme events. Ultimately, we tie spatial and temporal variations in the O3-meteorology relationships to the jet stream. The jet stream regulates the surface-level mean meridional flow, which affects fluxes of O3, heat, and moisture. These results provide significant gains in understanding the dominant role of transport on O3 variability and reconcile spatial variations in the relationships among O3, temperature, humidity, and the jet stream