Ammonia Trace gas analyer

U.S. Department of Agriculture, Agricultural Research Service, St. Paul, MN Location has a requirement for a Ammonia Trace Gas Annalyzer. Quoted Ammonia Trace Gas Annalyzers must meet the specsifications listed below. This instrument will be used in a micrometeorological application to determine half-hourly fluxes of ammonia between agricultural fields and the atmosphere, which requires measurement of the difference in concentration between two heights, typically 2 and 3 m above the surface. Air is sampled continuously from 4 inlets (2 in each of two adjacent fields) and routed to an instrument trailer, where solenoid valves sequentially switch each of them into the analyzer. The expected concentration differences can be quite small, often less than 1 nmol/mol, which imposes stringent requirements on both the precision and the sampling rate of the analyzer. The estimated requirement is a 10 s standard deviation of less than 1.0 ppbv, and a maximum sampling rate of 1 s or better. Expected ambient concentrations will often be near 1 ppbv, so the lower detection limit should be 1 ppbv or better.