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NO x instrument intercomparison for laboratory biomass burning source studies and urban ambient measurements in Albuquerque, New Mexico
Ist Teil von
Journal of the Air & Waste Management Association (1995), 2018-11, Vol.68 (11), p.1175-1189
Ort / Verlag
United States
Erscheinungsjahr
2018
Link zum Volltext
Quelle
Taylor & Francis Journals Auto-Holdings Collection
Beschreibungen/Notizen
Understanding nitrogen oxides (NO
= NO + NO
) measurement techniques is important as air-quality standards become more stringent, important sources change, and instrumentation develops. NO
observations are compared in two environments: source testing from the combustion of Southwestern biomass fuels, and urban, ambient NO
. The latter occurred in the urban core of Albuquerque, NM, at an EPA NCORE site during February-March 2017, a relatively clean photochemical environment with ozone (O
) <60 ppb for all but 6 hr. We compare two techniques used to measure NO
in biomass smoke during biomass burning source testing: light absorption at 405 nm and a traditional chemiluminescence monitor. Two additional oxides of nitrogen techniques were added in urban measurements: a cavity attenuated phase shift instrument for direct NO
, and the NO
chemiluminescence instrument (conversion of NO
to NO by molybdenum catalyst). We find agreement similar to laboratory standards for NO
, NO
, and NO comparing all four instruments (R
> 0.97, slopes between 0.95 and 1.01, intercepts < 2 ppb for 1-hr averages) in the slowly varying ambient setting. Little evidence for significant interferences in NO
measurements was observed in comparing techniques in late-winter urban Albuquerque. This was also confirmed by negligible NO
contributions as measured with an NO
instrument. For the rapidly varying (1-min) higher NO
concentrations in biomass smoke source testing, larger variability characterized chemiluminescence and absorption instruments. Differences between the two instruments were both positive and negative and occurred for total NO
, NO, and NO
. Nonetheless, integrating the NO
signals over an entire burn experiment and comparing 95 combustion experiments, showed little evidence for large systematic influences of possible interfering species biasing the methods. For concentrations of <2 ppm, a comparison of burn integrated NOx, NO
, and NO yielded slopes of 0.94 to 0.96, R
of 0.83 to 0.93, and intercepts of 8 to 25 ppb. We attribute the latter, at least in part, to significant noise particularly at low NO
concentrations, resulting from short averaging times during highly dynamic lab burns. Discrepancies between instruments as indicated by the intercepts urge caution with oxides of nitrogen measurements at concentrations <50 ppb for rapidly changing conditions. Implications: Multiple NO
measurement methods were employed to measure NO
concentrations at an EPA NCORE site in Albuquerque, NM, and in smoke produced by the combustion of Southwestern biomass fuels. Agreement shown during intercomparison of these NO
techniques indicated little evidence of significant interfering species biasing the methods in these two environments. Instrument agreement is important to understand for accurately characterizing ambient NO
conditions in a range of environments.