Efficacy of passive sampler collection for atmospheric NO isotopes under simulated environmental conditions.

RATIONALE

Nitrogen oxides or NO (NO = NO + NO ) play an important role in air quality, atmospheric chemistry, and climate. The isotopic compositions of anthropogenic and natural NO sources are wide-ranging, and they can be used to constrain sources of ambient NO and associated atmospheric deposition of nitrogen compounds. While passive sample collection of NO isotopes has been used in field studies to determine NO source influences on atmospheric deposition, this approach has not been evaluated for accuracy or precision under different environmental conditions.

METHODS

The efficacy of NO passive sampler collection for NO isotopes was evaluated under varied temperature and relative humidity (RH) conditions in a dynamic flux chamber. The precision and accuracy of the filter NO collection as nitrite (NO ) for isotopic analysis were determined using a reference NO gas tank and through inter-calibration with a modified EPA Method 7. The bacterial denitrifer method was used to convert 20 μM of collected NO or nitrate (NO ) into N O and was carried out on an Isoprime continuous flow isotope ratio mass spectrometer.

RESULTS

δ N-NO values determined from passive NO collection, in conditions of 11-34 °C, 1-78% RH, have an overall accuracy and precision of ±2.1 ‰, and individual run precision of ±0.6 ‰. δ O-NO values obtained from passive NO sampler collection, under the same conditions, have an overall precision of ± 1.3 ‰.

CONCLUSIONS

Suitable conditions for passive sampler collection of NO isotopes are in environments ranging from 11 to 34 °C and 1 to 78% RH. The passive NO isotope measurement technique provides an accurate method to determine variations in atmospheric δ N-NO values and a precise method for determining atmospheric δ O-NO values. The ability to measure NO isotopes over spatial gradients at the same temporal resolution provides a unique perspective on the extent and seasonality of fluctuations in atmospheric NO isotopic compositions. Copyright © 2017 John Wiley & Sons, Ltd.