Atmospheric ammonia measurement using a VUV/photo-fragmentation laser-induced fluorescence technique

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Abstract
Vacuum ultraviolet/photofragmentation laser-induced fluorescence has been demonstrated to be a highly specific and sensitive method for the quantitative measurement of atmospheric ammonia (NH3). The fluorescence detected in this approach results from the two 193-nm photon photofragmentation step NH3 ⇒ NH2 ⇒ NH(b1∑+) followed by the excitation of the NH(b1∑+) ⇒ NH(c1Π) transition via a 450-nm photon with final emission being observed from the NH(c1Π) ⇒ NH(a1Δ) transition at 325 nm. Limits of detection for the instrument presented here are b1∑+) ⇒ NH(c1Π) transition is sufficient to resolve 15NH3 and 14NH3 contributions for use in atmospheric tracer studies. Average ammonia measurements at Stone Mountain, GA, ranged from ≃110 pptv for air temperatures <5°C to ≃240 pptv for air temperatures ≥5°C over the period from Dec. 1987 to the end of Apr. 1988.