AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
LADCO Winter Nitrate Study – Sensitivity of 2009 Winter PM2.5 to Modeled Reductions in NOx and and Ammonia
CHARLES STANIER, Scott Spak, Yoo Jung Kim, Jessica Carlson, Jaemeen Baek, Gregory Carmichael, Abigail Fontaine, Mark Janssen, Michael Koerber, Nicole Riemer, Stephanie Shaw, University of Iowa
Abstract Number: 441 Working Group: Remote and Regional Atmospheric Aerosols
Abstract The Winter Nitrate Study was a measurement campaign with subsequent model-based analysis designed to understand wintertime episodes of elevated fine particulate (PM2.5) concentrations in the upper Midwest. These episodes occur several times per year throughout the upper Midwest, and hinder compliance with the 24-hour average federal air quality standard for PM2.5 of 35 micrograms per cubic meter. These episodes are often regional and are characterized by low wind speeds, near-freezing temperatures, and elevated levels of ammonium nitrate. From December 2008 to March 2009, an intensive monitoring campaign was conducted including continuous measurements of ammonia, ammonium, nitrate, nitric acid at an urban site (Milwaukee, Wisconsin), and an upwind rural site. We analyze results from 12 km resolution simulations using WRF v3.1 with CAMx v5.3 and CMAQ v4.7 chemical transport modeling to address the question: How effective are NOx, NH3, and SO2 emission reductions on PM2.5 concentrations? A method of observationally constraining total ammonia and total nitrate in conjunction with the forward sensitivity model is implemented and comparison to direct forward model sensitivity will be presented.
For the upper Midwest, equal percentage reductions of NH3 emissions and NOx emissions do not result in equal reductions in PM2.5, and the spatial patterns of the reductions are also different. NH3 emissions reductions lead to larger PM2.5 reductions than the corresponding NOx controls by a factor of about four for Mayville and Milwaukee. NOx reduction leads to PM2.5 reductions mainly west of the Mississippi in ammonia-rich regions. Ammonia controls are simulated to have reductions mainly east of the Mississippi river. These features (of NOx and NH3 reductions) are predicted in both the CAMx and CMAQ model runs. Localized reductions of both NH3 and NOx were simulated.