THE IMPACT OF UPPER TROPOSPHERIC DYNAMICS ON SURFACE AIR QUALITY OVER THE UNITED STATES

Abstract

Monitoring air quality and source attribution at the surface requires a vast understanding of radiative and dynamical effects in the lower atmosphere to capture influential processes affecting human health, the environment, and current pollutant standards. In order to accurately determine all sources impacting lower atmospheric composition, a more thorough comprehension of the dynamical, chemical, and radiative coupling of the stratosphere and troposphere is required. Particularly significant is the transport or exchange of trace gases (i.e. ozone), both natural and anthropogenic, between the stratosphere and troposphere also known as stratosphere-troposphere exchange (STE). During previous research campaigns, STE was found to contribute to the tropospheric ozone budget. In this work, a plan was designed to determine whether or not stratosphere-to-troposphere transport (STT) was a viable mechanism for elevated ozone at the surface, particularly in cases where unhealthy air quality conditions were detected. An investigation of several case studies in which high levels of surface ozone appear to originate from the stratosphere shows that a variety of dynamical processes from the boundary layer to the lower stratosphere are involved. Starting with the quasi-geostrophic equations of vertical and horizontal motion, dynamical parameters can be derived and evaluated from the North American Regional Reanalysis (NARR) meteorological fields. Reanalysis diagnostics, such as Q-vector, can locate the prevailing STT mechanism and capture the extent of vertical transport and mixing into the lower troposphere. Back trajectories from the UMBC-LT model released at the ground sites present additional support for stratospheric contribution to measured ozone levels. Along with the reanalysis dataset, a combination of satellite-retrieved and surface observations of chemical tracers were utilized to demonstrate the plausibility of a stratospheric source and to rule out anthropogenic surface contributions where possible. The practicality of Atmospheric InfraRed Sounder (AIRS), Tropospheric Emission Spectrometer (TES), and HIgh Resolution Dynamics Limb Sounder (HIRDLS) satellite observations to infer stratospheric transport as the probable source was tested for these case studies and the results supported dynamical evidence of STE using tracer correlations, as in the ozone-water vapor relationship. The overall strategy of implementing satellite, reanalysis, and surface measurements together provided strong evidence that unhealthy ozone anomalies at the ground were incurred primarily by STE in these events and setup future studies of resulting ozone signatures.