Transcript Monitoring Chemical Climate Change in America

Monitoring
Chemical Climate Change
in America
The Case for Ammonia
V. Bowersox, C. Lehmann, B. Larson
Acknowledge – R. Claybrooke
NADP Program Office
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.”
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
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
Sulfate, Nitrate & Ammonium Trends
Results:
Sulfate
Ammonium
Nitrate
Up Sig | Down Sig
7
0 | 132 106
124 58 | 15
2
70 23 | 69
17
Chemical Climate:
SO4/NH4/NH3/NO3/HNO3
 Inorganic SO4 has low volatility & reacts
readily with NH3 to form stable salts
• (NH4)2SO4 : NH4/SO4 = 1.00
• (NH4)3H(SO4)2 : NH4/SO4 = 0.75
• (NH4)HSO4 : NH4/SO4 = 0.50
• H2SO4 : NH4/SO4 = 0.00
 Ammonia-rich environment: NH4/SO4>1.00
(Seinfeld, Saxena,Tanner,etal.)
Chemical Climate:
SO4/NH4/NH3/NO3/HNO3
 NH4/NH3/NO3/HNO3 : distribution between
aerosol & gas phases depends on SO4, T, TD,
PHNO3, PNH3
 Ammonia-excess:
NH4-[(SO4+NO3+Cl) - (base cations)] > 0
(Blanchard, etal., 2000, JAWMA)
Monitoring
Chemical Climate Change
in America
The Case for Ammonia
 NH4 increased at ~90% (42% significant) of sites
& SO4 decreased at ~95% (76% significant) of sites
between 1985 and 2002.
These trends, accompanied by locally significant
changes in NO3, have increased the ammoniaexcess, altering the SO4/NH4/NH3/NO3/HNO3
chemistry in air and precipitation in the United
States.
Monitoring
Chemical Climate Change
in America
The Case for Ammonia
 The NADP provides a long-term high-quality
database for studying our chemical climate.