资源环境科技发展态势分析平台

Ozone (O-3) air pollution in Sequoia National Park (SNP) is among the worst of any national park in the US. SNP is located on the western slope of the Sierra Nevada Mountains downwind of the San Joaquin Valley (SJV), which is home to numerous cities ranked in the top 10 most O-3-polluted in the US. Here, we investigate the influence of emission controls in the SJV on O-3 concentrations in SNP over a 12-year time period (2001-2012). We show that the export of nitrogen oxides (NOx) from the SJV has played a larger role in driving high O-3 in SNP than transport of O-3. As a result, O-3 in SNP has been more responsive to NOx emission reductions than in the upwind SJV city of Visalia, and O-3 concentrations have declined faster at a higher-elevation monitoring station in SNP than at a low-elevation site nearer to the SJV. We report O-3 trends by various concentration metrics but do so separately for when environmental conditions are conducive to plant O-3 uptake and for when high O-3 is most common, which are time periods that occur at different times of day and year. We find that precursor emission controls have been less effective at reducing O-3 concentrations in SNP in springtime, which is when plant O-3 uptake in Sierra Nevada forests has been previously measured to be greatest. We discuss the implications of regulatory focus on high O-3 days in SJV cities for O-3 concentration trends and ecosystem impacts in SNP.