Ozone Modeling

The District has been applying photochemical models to simulate ozone beginning in 1989. Model applications and types of models used depend on a number of factors including District needs, the U.S. EPA and the California Air Resources Board (CARB) requirements, staff expertise, availability of appropriate models, and the nature of the problems being investigated.

From 1989 to 2006, the District’s photochemical modeling effort mostly focused on the preparation of the State Implementation Plan for 1-hour ozone. The U.S. EPA revoked its 1-hour ozone standard in 2006 and continued enforcing the 8-hour standard. Currently, the District marginally exceeds the U.S. EPA’s 8-hour standard. Marginal exceedance areas are not required to use photochemical models for attainment demonstration; however, the District is committed to continue working with neighboring districts and CARB to study regional ozone transport through the use of photochemical models. A preliminary ozone data analysis and modeling report is available:

Preliminary Ozone Data Analysis and Modeling Report 

Assessing the Effects of Climate Change on Bay Area Ozone

Studies by the International Panel on Climate Change suggest that the average global temperature may increase by two degrees Celsius from 2000 to 2050 due to climate change. It has also been suggested that future climate change scenarios could include more severe weather episodes (e.g., warmer and longer heat waves). This would have implications on the Bay Area’s ability to maintain healthy air quality, particularly for ozone, which is highly temperature-sensitive.

District staff assessed the impacts of the anticipated temperature increase in the Bay Area using emissions and meteorological data developed for an ozone episode (July 29–August 2, 2000). For the purpose of modeling, temperatures were increased uniformly 2 degrees Celsius over the modeling domain, biogenic emissions were estimated with increased temperatures, on-road vehicle emissions were adjusted, and the episode was simulated with these new inputs. Preliminary modeling results showed that the maximum increase in 8-hour average ozone was around 9 parts per billion. This is a significant increase since the Bay Area is currently marginally in nonattainment of the 8-hour ozone standard. At the current rate of emissions control, the projected increase in ozone due to climate change from 2000 to 2050 would offset about 15 years of progress in reducing ambient ozone levels.