Ammonia sources in the California South Coast Air Basin and their impact on ammonium nitrate formation

• Published in: Geophysical research letters Vol. 39; no. 7
• Main Authors: Nowak, J. B., Neuman, J. A., Bahreini, R., Middlebrook, A. M., Holloway, J. S., McKeen, S. A., Parrish, D. D., Ryerson, T. B., Trainer, M.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01.04.2012; American Geophysical Union; John Wiley & Sons, Inc
• Subjects: Agriculture; Air pollution; Ammonia; Ammonium; Ammonium nitrate; Atmospheric aerosols; Atmospheric sciences; automobile emissions; CalNex 2010; dairy farm emissions; Earth sciences; Earth, ocean, space; Emission inventories; Exact sciences and technology; Geobiology; Motor vehicles; South Coast Air Basin; Systems science; Troposphere; Vehicle emissions; United States; California; INE, USA, California; ammonia(compound); aerosols; NOAA; air; North America; Emission inventory; Ammonia; Rotaliacea; foraminifera; three-dimensional models; Ammonium nitrate; Invertebrata; Protista; Mixing ratio; strategy; Rotaliina
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2012GL051197

Observations from the NOAA WP‐3D aircraft during CalNex in May and June 2010 are used to quantify ammonia (NH3) emissions from automobiles and dairy facilities in the California South Coast Air Basin (SoCAB) and assess their impact on particulate ammonium nitrate (NH4NO3) formation. These airborne measurements in the SoCAB are used to estimate automobile NH3 emissions, 62 ± 24 metric tons day−1, and dairy facility NH3 emissions, 33 ± 16 to 176 ± 88 metric tons day−1. Emission inventories agree with the observed automobile NH3:CO emission ratio, but substantially underpredict dairy facility NH3 emissions. Conditions observed downwind of the dairy facilities were always thermodynamically favorable for NH4NO3 formation due to high NH3 mixing ratios from the concentrated sources. Although automobile emissions generated lower NH3 mixing ratios, they also can thermodynamically favor NH4NO3 formation. As an aerosol control strategy, addressing the dairy NH3 source would have the larger impact on reducing SoCAB NH4NO3 formation. Key Points Mass of SoCAB ammonia emissions is similar from automobile and dairy sources SoCAB dairy ammonia emissions are underrepresented in inventories Dairy ammonia emissions have larger impact on SoCAB ammonium nitrate formation