Impact of Southern California anthropogenic emissions on air quality in the Western US
Abstract
Observations in mid July 2009 identified that Southern California (SoCal) pollutants were responsible for the ozone "spikes" at downwind states in the Western US ~48 hours later (Langford et al., 2010). The impact of SoCal anthropogenic emissions on downwind states air quality still needs further study, including the frequency, intensity, and its relationship with surface ozone exceedence. As the westerly winds that lead to the transport of pollution from the eastern Pacific to inland Western US can pick up the local pollution over the Pacific states on its way, it is also important to explore whether the transport of SoCal emissions can occur together with intercontinental transport of pollution and stratospheric intrusion. The findings will benefit the tightening of future air quality standards and the strategies of reducing pollution impacts in the intermountain areas. We modeled the Western US air quality during the CalNex field campaign period in May-June 2010 using the STEM chemical transport model on a 12 km horizontal resolution grid. The simulation is evaluated using available observations (surface, aircraft, ozonesondes and satellites). Sensitivity simulations in which the SoCal anthropogenic emissions were turned off demonstrate that SoCal emissions can be transported to the intermountain regions. The instantaneous contributions to surface ozone over these states (e.g., Arizona, Utah, Colorado) can be as high as 10-20 ppb, and are overall stronger during the periods that were found affected by the extra-regional (e.g., Asian) emission sources and the upper troposphere/lower stratosphere (UT/LS) ozone. The STEM base simulation and sensitivity results differ slightly when the model was driven by different meteorological fields (using different WRF model configurations), and the responses over the urban and rural/remote regions are evaluated. Furthermore, ozone observations from various platforms (surface, aircraft, TES) over SoCal and intermountain regions are compared for consistency and their utility in representing the transport. These results are compared with 1) the impact of northwestern anthropogenic emissions on downwind states in the Western US; and 2) the Carbon Monoxide import/export budgets generated by STEM tagged tracers (which are evaluated by surface measurements and aircraft/satellite profiles (MOPITT, TES, AIRS)). References Langford, A. O., C. J. Senff, R. J. Alvarez II, R. M. Banta, and R. M. Hardesty (2010), Long-range transport of ozone from the Los Angeles Basin: A case study, Geophys. Res. Lett., 37, L06807, doi: 10.1029/2010GL042507.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.A21B0046H
- Keywords:
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- 0365 ATMOSPHERIC COMPOSITION AND STRUCTURE / Troposphere: composition and chemistry;
- 0368 ATMOSPHERIC COMPOSITION AND STRUCTURE / Troposphere: constituent transport and chemistry