Wintertime ammonium nitrate aerosol pollution is a severe air quality issue affecting both developed and rapidly urbanizing regions from Europe to East Asia. In the United States, it is acute in western basins subject to inversions that confine pollutants near the surface. Measurements and modeling of a wintertime pollution episode in Salt Lake Valley, Utah, demonstrate that ammonium nitrate is closely related to photochemical ozone through a common parameter, total odd oxygen, Ox,total. We show that the traditional nitrogen oxide and volatile organic compound (NOx-VOC) framework for evaluating ozone mitigation strategies also applies to ammonium nitrate. Despite being nitrate-limited, ammonium nitrate aerosol pollution in Salt Lake Valley is responsive to VOCs control and, counterintuitively, not initially responsive to NOx control. We demonstrate simultaneous nitrate limitation and NOx saturation and suggest this phenomenon may be general. This finding may identify an unrecognized control strategy to address a global public health issue in regions with severe winter aerosol pollution.
Bibliographical noteFunding Information:
The authors thank NOAA Aircraft Operations, particularly Jason Clark, Rob Mitchell, Rob Militec, and Lindsay Norman, and the Utah Division of Air Quality, particularly Chris Pennell, Brock LeBaron, and Patrick Barrickman. The authors acknowledge Gail Tonnesen, Stuart McKeen, Sebastian Hoch, Eric Crosman, Michael Trainer, and David Parrish for helpful discussions. This is NOAA PMEL contribution number 4819. The views expressed in this article are those of the authors and do not necessarily represent the views or policies of the U.S. Environmental Protection Agency. This study was partially supported by Utah State Contract 170856. M. B., J. C. L., and S. S. B. initiated and supervised the UWFPS study. C. C. W., E. E. M., R. B., K. S. D., W. P. D., D. L. F., A. F., L. G., R. L., A. M. M., D. B. M., A. M., J. G. M., T. P. R., J. A. T., L. C. V., A. R. W., M. B., and S. S. B. collected and curated the UWFPS data. J. A. dG., P. K. Q., J. M. R., P. R. V., R. J. W., C. W., B. Y., and S. S. B. collected and curated the UBWOS data. J. B. G. and B. H. L. curated and validated the UWFPS data. C. C. W., E. E. M., P. M. E., and S. S. B. developed the split box model. C. C. W. and S. S. B. wrote the manuscript. All authors contributed to and edited the manuscript. Authors declare no competing interests. All raw data can be accessed on the UWFPS website (https://www.esrl.noaa.gov/csd/ groups/csd7/measurements/ 2017uwfps/). The DSMACC box model may be downloaded for free online (https://github.com/barronh/ DSMACC).
- Salt Lake City
- ammonium nitrate aerosol
- box modeling
- odd oxygen
- wintertime air quality