Efficacy of passive sampler collection for atmospheric NO2 isotopes under simulated environmental conditions.

Abstract

Nitrogen oxides or NOx (NOx = NO + NO2 ) play an important role in air quality, atmospheric chemistry, and climate. The isotopic compositions of anthropogenic and natural NO2 sources are wide-ranging, and they can be used to constrain sources of ambient NO2 and associated atmospheric deposition of nitrogen compounds. While passive sample collection of NO2 isotopes has been used in field studies to determine NOx source influences on atmospheric deposition, this approach has not been evaluated for accuracy or precision under different environmental conditions. The efficacy of NO2 passive sampler collection for NO2 isotopes was evaluated under varied temperature and relative humidity (RH) conditions in a dynamic flux chamber. The precision and accuracy of the filter NO2 collection as nitrite (NO2- ) for isotopic analysis were determined using a reference NO2 gas tank and through inter-calibration with a modified EPA Method 7. The bacterial denitrifer method was used to convert 20 μM of collected NO2- or nitrate (NO3- ) into N2 O and was carried out on an Isoprime continuous flow isotope ratio mass spectrometer. δ15 N-NO2 values determined from passive NO2 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 ‰. δ18 O-NO2 values obtained from passive NO2 sampler collection, under the same conditions, have an overall precision of ± 1.3 ‰. Suitable conditions for passive sampler collection of NO2 isotopes are in environments ranging from 11 to 34 °C and 1 to 78% RH. The passive NO2 isotope measurement technique provides an accurate method to determine variations in atmospheric δ15 N-NO2 values and a precise method for determining atmospheric δ18 O-NO2 values. The ability to measure NO2 isotopes over spatial gradients at the same temporal resolution provides a unique perspective on the extent and seasonality of fluctuations in atmospheric NO2 isotopic compositions. Copyright © 2017 John Wiley & Sons, Ltd.