Analysis of Elevated Ozone in the Small City of Spokane, WA with Respect to a Lower Ozone Standard

Analysis of Elevated Ozone in the Small City of Spokane, WA
with respect to a Lower Ozone Standard

Eric M. Lopato, Vikram Ravi, Serena Chung, and Brian Lamb

Washington State University – Laboratory for Atmospheric Research

Abstract

The National Ambient Air Quality Standard (NAAQS) for daily maximum 8-hour ozone was recently reduced from 75 ppb to 70 ppb, which increases the possibility for exceedances in areas not previously known for ozone issues.  The Spokane – Coeur d’Alene airshed in eastern WA, northern ID, is an example where elevated ozone has occurred at three different ozone monitoring sites in recent years.  To investigate the nature of elevated ozone episodes in the Spokane region, we selected an episode spanning July 1-14, 2012 when there was no obvious impact from wildland fires on ozone in the region.    The AIRPACT-5 forecast system using the WRF-CMAQ modeling suite was used for the simulations.  HYSPLIT back trajectories were created and combined with simulated ozone and precursor concentrations in order to investigate the production of ozone from source to monitor locations.  Meandering back trajectories and the simultaneous occurrence of peak ozone levels at all three monitor sites, including one urban site and two rural sites located northeast and southwest of the urban center, suggested elevated ozone was produced under stagnant summertime conditions where precursors from the Spokane-Coeur d’Alene corridor lead to widespread ozone production in the region.  Preliminary data analysis indicates the area is primarily VOC-limited with respect to ozone production measured at both urban and rural sites. To further analyze for VOC-NOx sensitivity, we will also present results from two additional scenarios with anthropogenic NOx and VOCs each reduced by 50%, and the consequent impact on ozone.