A Measurement of Total Reactive Nitrogen, NO_y, together with NO_2, NO, and O_3 via Cavity Ring-down Spectroscopy

摘要

We present a sensitive, compact detector that measures total reactive nitrogen (NO_y), as well as NO_2, NO, and O_3. In all channels, NO_2 is directly detected by laser diode based cavity ring-down spectroscopy (CRDS) at 405 nm. Ambient O_3 is converted to NO_2 in excess NO for the O_3 measurement channel. Likewise, ambient NO is converted to NO_2 in excess O_3. Ambient NO_y is thermally dissociated at ～700 ℃ to form NO_2 or NO in a heated quartz inlet. Any NO present in ambient air or formed from thermal dissociation of other reactive nitrogen compounds is converted to NO_2 in excess O_3 after the thermal converter. We measured thermal dissociation profiles for six of the major NO_y components and compared ambient measurements with other instruments during field campaigns in Utah and Alabama. Alabama measurements were made in a rural location with high biogenic emissions, and Utah measurements were made in the wintertime in unusual conditions that form high ozone levels from emissions related to oil and gas production. The NO_y comparison in Alabama, to an accepted standard measurement method (a molybdenum catalytic converter/chemiluminescence instrument), agreed to within 12%, which we define as an upper limit to the accuracy of the NO_y channel. The 1σ precision is ＜30 pptv at 1 s and ＜4 pptv at 1 min time resolution for all measurement channels. The accuracy is 3% for the NO_2 and O_3 channels and 5% for the NO channel. The precision and accuracy of this instrument nuke it a versatile alternative to standard chemiluminescence-based NO_y instruments.