Seminar

Abstract

p>Understanding the global sources of local ozone pollution is crucial for designing appropriate control policies to better protect public health and welfare. This talk will draw upon analysis of satellite and in situ measurements with a fully coupled global chemistry-climate model (GFDL AM3) to explore the role of naturally occurring stratospheric ozone intrusions, wildfires, and rising Asian anthropogenic emissions in driving extreme events, inter-annual variability, and long-term changes of tropospheric and surface ozone over the United States in the past 30 years. Leveraging a rich suite of measurements from the CalNex field campaign in spring 2010, we find that a high-resolution (~50x50 km2) version of the GFDL AM3 model captures the principle features of observed ozone, both at the surface and aloft. During several episodes of high surface ozone in spring 2010, transport of stratospheric ozone and Asian pollution to the surface can contribute 30-55 ppbv and 8-15 ppbv of ozone, respectively, in parts of California and the central western USA. These new findings imply substantial non-local influences on compromising attainment of U.S. National Ambient Air Quality Standard (NAAQS) for ground-level ozone. We further use ~200x200 km2 GFDL AM3 simulations for 1980-2010 and observational records to examine how typical conditions were in spring 2010. Preliminary analysis suggests that stratosphere-to-troposphere exchange dominates inter-annual variability of free tropospheric ozone over Pacific North America associated with ENSO (i.e.1983-1984, 1998-1999, and 2009-2010) and other factors. In spring, rising Asian emissions of ozone precursors primarily contribute to long-term increasing trend of ozone over the western USA. In summer, ozone produced from Siberia and North American boreal fire emissions is the major driver of inter-annual variability of background ozone over the northwest and northeastern U.S. (i.e. higher in 1998, 2002, 2003, 2004, and 2010). We expect that the associated variability should provide insights regarding potential responses to climate shifts as well as inform air quality planning and control strategies.