Fast and Efficient Atmospheric NO 2 Collection for Isotopic Analysis by a 3D-Printed Denuder System.

Being major species of atmospheric reactive nitrogen, nitrogen oxides (NO x = NO + NO 2 ) have important implications for ozone and OH radical formation in addition to nitrogen cycles. Stable nitrogen isotopes (δ 15 N) of NO x have been sought to track NO x emissions and NO x chemical reactivities in the atmosphere. The current atmospheric NO x collection methods for isotopic analysis, however, largely suffer from unverified collection efficiency and/or low collection speed (<10 L/min). The latter makes it difficult to study δ 15 N(NO x ) in pristine regions with low NO x concentrations. Here, we present a three-dimensional (3D)-printed honeycomb denuder (3DP-HCD) system, which can effectively collect atmospheric NO 2 (a major part of NO x ) under a variety of laboratory and field conditions. With a coating solution consisting of 10% potassium hydroxide (KOH) and 25% guaiacol in methanol, the denuder system can collect NO 2 with nearly 100% efficiency at flow rates of up to 70 L/min, which is 7 times higher than that of the existing method and allows high-resolution (e.g., diurnal or finer resolution) NO 2 collection even in pristine sites. Besides, the δ 15 N of NO 2 collected by the 3DP-HCD system shows good reproducibility and consistency with the previously tested method. Preliminary results of online NO oxidation by a chrome trioxide (CrO 3 ) oxidizer for simultaneous NO and NO 2 collection are also presented and discussed.