Long-period atmospheric oscillations can have effects on summertime air quality in the Eastern US, based on two studies from Harvard researchers, and these effects can be relevant to air quality management.
The first analysis shows that summertime air quality in the eastern US depends on the sea-surface temperature in the North Atlantic Ocean. Researchers used observations of air quality, meteorology, and seas-surface temperature, as well as climate simulations for this study. The results point to a multi-decadal variability cycle in surface air quality driven by the Atlantic Multidecadal Oscillation (AMO), with a period of about 70 years. The impact of The AMO effect on air quality, identified over the half-period from cool to warm conditions, was an ozone increase of 1-4 ppb and a PM2.5 increase of 0.3-1.0 mg/m3 over much of the Eastern US. The effect is mediated by the prevalence of stagnant weather conditions during the AMO warm phase. Future transitions to the cool phase could mitigate the climate penalty on air quality, making this mechanism relevant for air quality planning.
The second shows that summertime ozone levels in the Eastern US are affected by El Niño events, based on research by the Harvard ACE Center (835872). The analysis focused on maximum daily 8-hr ground-level ozone concentrations during the summers between 1980 and 2016. The effect depends on conditions leading to the reduced transport of cleaner air into the Atlantic states, greater air subsidence, less precipitation and increased solar radiation. At the same time, conditions during event years promote the flow of cleaner air from the south into the south-central region. The overall impact of these flow patterns results in an increas of 1-2 ppb of ozone in the Atlantic states and a decrease of 0.5-2.0 ppb in the south-central states per each standard deviation increase in the El Niño 1 + 2 index. These effects can be predicted up to 4 months in advance, which may help regional and state air quality planning.