Improved acid trap methodology for determining ammonia volatilization in wind tunnel experiments

Nitrogen loss through ammonia volatilization is an environmental and economic concern. When acid traps are used with wind tunnels to measure ammonia volatilization, loss of solution volume is observed. A field study was conducted to determine if solution loss from acid traps was due to either selective loss of water through evaporation, loss of bulk solution, or a combination of the two processes. Two methods for calculating air flow volume through the acid traps were also examined. Solution losses from acid traps averaged 40 mL from an initial 100 mL, and ammonium concentration increased in close accordance with the dilution–concentration relationship for solutions. Hence, solution loss was due to evaporation of the water in the acid trap with virtually no ammonium loss. Hence the liquid volume in the samples must be measured and used in the calculations of ammonia volatilization losses. Failure to correct for the reduced volumes resulted in 9 to 224% overestimation of ammonium concentrations. Air flow volumes through acid traps were underestimated by 18.5% when initial and final air flow rates were used compared with continuous cumulative flow measurements. Therefore both cumulative flows and accounting for evaporation loss from acid traps help to ensure that treatment differences are not masked by the inherent variability in the field-based measurements.