Meteorological Controls on Spring Ozone Variability in Lower Troposphere in Northeast U.S.: Implications for Stratospheric Intrusions

We use a correlation-based classification algorithm (map typing method) to identify the major synoptic-scale weather patterns modulating the spatial and temporal variation of ozone (O3) in the lower troposphere in the Northeast U.S. during springtime. A 5-year data set comprised of O3 observations from the EPA AIRNOW and the AIRMAP networks that includes an elevated background monitoring site in rural New England (Mount Washington Observatory - MWO, 44.3N, 71.3W, 1910m asl) is used. The meteorological data consists of hemispheric analyses from the NCEP Global Final Analysis, surface weather maps from Unisys Weather (http://weather.unisys.com/), local surface and sounding observations from NOAA/NWS sites, and surface observation from the AIRMAP sites. Using these data sets, we seek to quantify the relative contributions of different synoptic-scale circulation processes to the O3 enhancement in the lower troposphere of Northeast U.S. We estimate that the dynamical effect (resulting from upper air subsidence) is about one third of the photochemical effect, with the former occurring with lower frequency and less O3 enhancement. Case studies of O3 events observed at MWO are also discussed to illustrate how short-term O3 varies with synoptic conditions. Our data analysis forms a basis for evaluating a 3-D chemistry transport model's ability to reproduce synoptic-scale O3 variability and quantify the contributions of different processes influencing O3 on the regional scale.