Modeling Regional & Global Atmospheric Chemistry Mechanisms: Observing Adverse Respiratory Health Effects due to Tropospheric Ozone Air Pollution from Modeling Output

Emily Saunders
  5 Feb, 10 a.m., in 2890

Regional air quality forecasts may be improved through the use of global model simulations to provide boundary conditions (BCs) to regional air quality models. The most important advantage of using global model BCs is that these BCs can bring time-varied external signals to the regional domain, and reflect certain event information, such as biomass burning, stratospheric intrusion, and Asian air mass inflow. These observations suggest that the use of global model BCs can improve regional air quality predictions. It also points out that further improvement in regional model predictions will require efforts to reduce the uncertainty in the global model BCs. Additional uncertainties are introduced in this importing process because of the uncertainties in the global models, and because of differences in resolution between the global and regional models, and differences in model formations, such as chemical mechanisms.

The main goal of this research project was to create a new gas-phase chemical mechanism for global atmospheric chemistry models, the Global Atmospheric Chemistry Mechanism (GACM) that is based on the Regional Atmospheric Chemistry mechanism, version 2 (RACM2). Improved global atmospheric chemistry models with GACM can be used to supply better initial and BCs to regional air quality models especially those that use RACM2 because GACM and RACM2 are designed to be highly compatible representations of atmospheric chemistry.

GACM includes marine chemistry reactions to simulate marine environments better while maintaining a compact size. For GACM some volatile organic compound (VOC) chemistry was simplified to make room the additional marine chemistry and to maintain computational efficiency. RACM2 and GACM were compared and evaluated through simple box modes and the Weather Research & Forecasting Model coupled with chemistry (WRF-Chem). WRF-Chem allowed RACM2 and GACM tropospheric ozone simulations to be compared under more realistic world conditions. California’s South Coast Air Basin (i.e. the SoCAB region) was used as a testbed for the WRF-Chem simulations. All of these simulations showed the compatibility of RACM2 and GACM and that these two mechanisms will work well in a global-regional modeling system where GACM provides boundary conditions to a regional scale model.

As a further test of the compatibility of RACM2 and GACM the WRF-Chem simulations were processed with the EPA’s Environmental Benefits Mapping & Analysis Program – Community Edition (BenMAP-CE) to estimate the respiratory related human health impacts and costs within the SoCAB region. The WRF-Chem simulations with GACM and RACM2 gave very similar estimates of the negative respiratory health impacts and the cost of those health impacts. Further, our work shows that BenMAP-CE could be used to forecast routinely daily changes in air quality health impacts and costs.

In closing, GACM will be applicable to current global models and can be used in conjunction with RACM2 based or other regional modeling systems to more accurately predict the amount of ozone formed in highly polluted urban local communities especially on the west coast of the United States.