7.9
Measurement and Modeling of Ammonia Flux and Dry deposition Velocity from near–Surface Concentration Gradient Measurement Over Natural Surfaces in North Carolina
Sharon B. Phillips, North Carolina State University, Raleigh, NC; and S. P. Arya and V. P. Aneja
The primary focus of our experimental and modeling study is on the emission and dry deposition fluxes of ammonia, using micrometeorological technique over different types of agricultural and natural surfaces in North Carolina where animal farms and waste storage and treatment lagoons (which are known to emit ammonia) are located. Ammonia concentrations are measured at two heights (2 and 6m) above the surface employing an arrangement of a Thermo Environmental Instruments, Inc. (TEI) Model 42S (modified to a Model 17) and Model 17C chemiluminescent nitrogen oxides (NOx)-ammonia (NH3) analyzers along with a solenoid for each analyzer to alternate measurements between the two elevations. A switching frequency of 10 minutes allows hourly gradient measurements of three 10-minute intervals for each height. An average of the last 6 minutes of concentration data is considered in order to minimize measurement errors related to the analyzer's resonse time (~2 to 3 minutes). A scatterplot and linear regression of the measured NH3 concentrations by the two chemiluminescent analyzers showed good agreement between the two with significant correlations during both daytime (r2=0.91) and nighttime (r2=0.89) periods. Simultaneously, mean winds and temperatures are also measured at the same two heights. Micrometeorological gradient and modified Bowen-ratio methods are used, in conjunction with the Monin-Obukhov similarity theory, to estimate the vertical flux and dry deposition velocity of ammonia under different meteorological conditions. Gradient measurements will also be made over different types of natural surfaces near ammonia sources under a wide range of wind and atmospheric stability conditions. We will also study diurnal and seasonal variations of ammonia flux and dry deposition velocity.
Session 7, integrated modeling/measurement systems for emissions and air quality predictions (Parallel with Joint Sessions J3 & J4)
Thursday, 23 May 2002, 9:00 AM-12:57 PM
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