Wood Stove Curtailment Forecasting in Portola, California

The town of Portola, California, situated in the northern Sierra Nevada range, has been designated as being in nonattainment of the federal annual fine particulate matter (PM_2.5) standard since 2015. Residential burning, combined with strong wintertime temperature inversions, light winds, and terrain blocking, lead to frequent high-PM_2.5 episodes in this rural mountain town. In an effort to combat high PM_2.5 levels driven by residential wood smoke, the Northern Sierra Air Quality Management District (NSAQMD) has taken proactive steps to improve local air quality. In 2016, the District implemented a wood stove replacement program, which offers free replacement of non-U.S. Environmental Protection Agency (EPA)-certified wood stoves with new, efficient, cleaner-burning EPA-certified devices. This program has successfully replaced over 600 older wood stoves in a town with a population of just over 2,000.

In addition to the wood stove replacement program, the district has implemented a wood stove curtailment (WSC) program, which aims to reduce burning activity when meteorological conditions are forecast to be conducive to pollutant accumulation in the Portola region. When PM_2.5 concentrations are forecast to exceed a given threshold, the NSAQMD issues a curtailment day, and residents are encouraged to use other sources of heat, if possible. Sonoma Technology meteorologists issue daily wintertime PM_2.5 forecasts in support of this program. To help guide forecasting efforts, Sonoma Technology meteorologists have developed a machine-learning-based forecast tool that uses meteorological model data to predict daily 24-hour average PM_2.5 concentrations up to five days in the future, as well as the likelihood of a WSC threshold exceedance. Assisted by these tools, Sonoma Technology meteorologists achieved a next-day forecast accuracy of 84% with respect to Portola’s curtailment threshold during the 2023-24 curtailment season.

PM_2.5 Air Quality Index levels have improved greatly with the implementation of these programs. The average percentage of wintertime days above the federal 24-hour PM_2.5 standard dropped from 60% to 32% with the wood stove replacement program, and was further reduced to only 8% with the combined effects of the stove replacement and WSC programs. This talk will focus on air quality forecasting and tool development in support of the WSC program, as well as Sonoma Technology’s coordination with NSAQMD to issue action days for Portola.