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Monitoring Chemical Climate Change in America The Case for Ammonia V. Bowersox, C. Lehmann, B. Larson Acknowledge – R. Claybrooke NADP Program Office
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Air and Rain– the Beginnings of a Chemical Climatology by Robert Angus Smith (1872) “When the sulphuric acid increases more rapidly than the ammonia, the rain becomes acidic.”
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Ammonia/Ammonium Trends Methods: trends period: 1985 through 2002 applied Seasonal Kendall Trend Test meteorological seasons (Dec-Feb, etc.) applied four NADP data completeness criteria to accept/reject a season & a site calculated Sen’s Estimator to quantify trends
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Ammonia/Ammonium Trends Results: 139 sites met completeness criteria for the 18-year trends period Ammonium Increasing 124 (89.2%) sites 58 (41.7%) significant (p<0.05) Ammonium Decreasing 15 (10.8%) sites 2 (1.4%) significant
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Sulfate, Nitrate & Ammonium Trends Results: UpSig |Down Sig Sulfate 7 0 | 132 106 Ammonium124 58 | 15 2 Nitrate 70 23 | 69 17
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Chemical Climate: SO 4 /NH 4 /NH 3 /NO 3 /HNO 3 Inorganic SO 4 has low volatility & reacts readily with NH 3 to form stable salts (NH 4 ) 2 SO 4 : NH 4 /SO 4 = 1.00 (NH 4 ) 3 H(SO 4 ) 2 : NH 4 /SO 4 = 0.75 (NH 4 )HSO 4 : NH 4 /SO 4 = 0.50 H 2 SO 4 : NH 4 /SO 4 = 0.00 Ammonia-rich environment: NH 4 /SO 4 >1.00 (Seinfeld, Saxena,Tanner,etal.)
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Chemical Climate: SO 4 /NH 4 /NH 3 /NO 3 /HNO 3 NH 4 /NH 3 /NO 3 /HNO 3 : distribution between aerosol & gas phases depends on SO 4, T, T D, P HNO3, P NH3 Ammonia-excess: NH 4 -[(SO 4 +NO 3 +Cl) - (base cations)] > 0 (Blanchard, etal., 2000, JAWMA)
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NH 4 increased at ~90% (42% significant) of sites & SO 4 decreased at ~95% (76% significant) of sites between 1985 and 2002. Monitoring Chemical Climate Change in America The Case for Ammonia These trends, accompanied by locally significant changes in NO 3, have increased the ammonia- excess, altering the SO 4 /NH 4 /NH 3 /NO 3 /HNO 3 chemistry in air and precipitation in the United States.
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Monitoring Chemical Climate Change in America The Case for Ammonia The NADP provides a long-term high-quality database for studying our chemical climate.
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