Unraveling the sources of ground level ozone in the Intermountain Western United States using Pb isotopes

• Published in: The Science of the total environment 2015-10, Vol.530-531, p.519-525
• Main Authors: Christensen, John N., Weiss-Penzias, Peter, Fine, Rebekka, McDade, Charles E., Trzepla, Krystyna, Brown, Shaun T., Gustin, Mae Sexauer
• Format: Article
• Language: English
• Subjects: Aerosols; Air Pollutants - analysis; Air Pollution - statistics & numerical data; Atmosphere - chemistry; Environmental Monitoring; Environmental Policy; Lead - analysis; Long-range transport; Los Angeles; Nevada; Ozone; Ozone - analysis; Pb isotopes; United States; United States Environmental Protection Agency
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2015.04.054

Ozone as an atmospheric pollutant is largely produced by anthropogenic precursors and can significantly impact human and ecosystem health, and climate. The U.S. Environmental Protection Agency has recently proposed lowering the ozone standard from 75ppbv (MDA8=Maximum Daily 8-Hour Average) to between 65 and 70ppbv. This will result in remote areas of the Intermountain West that includes many U.S. National Parks being out of compliance, despite a lack of significant local sources. We used Pb isotope fingerprinting and back-trajectory analysis to distinguish sources of imported ozone to Great Basin National Park in eastern Nevada. During discrete Chinese Pb events (>1.1ng/m3 & >80% Asian Pb) trans-Pacific transported ozone was 5±5.5ppbv above 19year averages for those dates. In contrast, concentrations during regional transport from the Los Angeles and Las Vegas areas were 15±2ppbv above the long-term averages, and those characterized by high-altitude transport 3days prior to sampling were 19±4ppbv above. However, over the study period the contribution of trans-Pacific transported ozone increased at a rate of 0.8±0.3ppbv/year, suggesting that Asian inputs will exceed regional and high altitude sources by 2015–2020. All of these sources will impact regulatory compliance with a new ozone standard, given increasing global background. [Display omitted] •Ozone can significantly impact human and ecosystem health and climate.•Pb isotopes and back-trajectory analysis were used to distinguish sources of O3.•Baseline concentrations in the Western US are ~54ppbv.•During discrete Asia events O3 increased by 5±5.5ppbv and during S CA events by 15±2ppbv.•Data indicate that Asian ozone inputs will exceed other sources by 2015–2020.