A sensitive, compact detector measures total reactive nitrogen (NOy), as well as NO2, NO, and O3. In all channels, NO2 is directly detected by laser diode based cavity ring-down spectroscopy (CRDS) at 405 nm. Ambient O3 is converted to NO2 in excess NO for the O3 measurement channel. Likewise, ambient NO is converted to NO2 in excess O3. Ambient NOy is thermally dissociated at 700 C to form NO2 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 NO2 in excess O3 after the thermal converter. The precision and accuracy of this instrument make it a versatile alternative to standard chemiluminescence-based NOy instruments.
The instrument has lower power, size, weight, and vacuum requirements than a chemiluminescence-based instrument while approaching its sensitivity, precision and time response. In the NOy CRDS instrument of the present invention, NOy and its components are converted into NO2 by thermal decomposition (TD) in a fused silica inlet (henceforth referred to as quartz, following convention), followed by the addition of ozone to convert NO to NO2. NO2 is then measured using a cavity ring-down spectroscopy instrument, utilizing a 405 nm laser. The device may comprise four parallel channels, each driven by the same laser, to measure NO, NO2, NOy and O3, respectively, such that overall NOy may be measured, as well as its components NO, NO2, as well as ozone (O3).
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