Department of Chemistry, Brown University, 324 Brook Street, Providence, Rhode Island 02912, United States.
Department of Earth, Environmental, and Planetary Sciences and Institute at Brown for Environment and Society, Brown University, 324 Brook Street, P.O. Box 1846, Providence, Rhode Island 02912, United States.
Anal Chem. 2020 Dec 15;92(24):16079-16088. doi: 10.1021/acs.analchem.0c03696. Epub 2020 Dec 2.
Stable isotopic composition of atmospheric nitrate (nitric acid (HNO) + particulate nitrate (pNO)) provides a higher-order dimensional analysis of critical atmospheric components, enabling a process-level understanding of precursor emissions, oxidation chemistry, aerosol acidity, and depositional patterns. Current methods have not been evaluated for their ability to accurately speciate and determine nitrogen (δN) and oxygen (δO and ΔO) isotope compositions for gaseous and particle phases. Suitability of a denuder-filter sampling system for the collection of speciated HNO and pNO for off-line concentration and isotopic determination was tested using both laboratory and field collections. Honeycomb denuders coated with either NaCl or NaCO solutions were used to collect HNO. Laboratory experiments found that both coating solutions quantitatively collected HNO, with the NaCO solution demonstrating a higher operative capacity (>1470 μg of HNO; = 25) compared to the NaCl solution (∼750 μg of HNO; = 25). The precision values for laboratory-tested HNO collections are ±0.6‰ and ±1.2‰ for δN and δO for the NaCl solution and ± 0.8‰ and ±1.2‰ for the NaCO solution. Replicate (urban) samples indicate that the NaCO solution is significantly less selective for HNO collection than the NaCl solution. Nylon filters were found to collect efficiently and retain laboratory-generated NaNO and NHNO particles, with maximum standard deviations for δN and δO of ±0.3‰ and ±0.3‰, respectively. Field replicates, while predictably more variable, also show consistency for δN and δO of ±0.6‰ and ±1.3‰ for particulate species, respectively. Recommended methods for field collections of speciated HNO and pNO for isotopic measurements would best utilize the NaCl solution and Nylon filters.
大气硝酸盐（硝酸（HNO）+颗粒硝酸盐（pNO））的稳定同位素组成提供了对关键大气成分的高阶维度分析，使我们能够深入了解前体排放、氧化化学、气溶胶酸度和沉积模式等过程。目前的方法尚未经过评估，无法准确地对气体相和颗粒相进行氮（δN）和氧（δO 和ΔO）同位素组成的形态分析。使用实验室和野外收集来测试使用浸渍滤器采样系统收集气态和颗粒态特定形态 HNO 和 pNO 的适用性，以便离线浓缩和同位素测定。使用涂有 NaCl 或 NaCO 溶液的蜂窝状浸渍滤器收集 HNO。实验室实验发现，两种涂层溶液都可以定量收集 HNO，而 NaCO 溶液的操作能力（>1470 μg 的 HNO； = 25）高于 NaCl 溶液（∼750 μg 的 HNO； = 25）。经过实验室测试的 HNO 收集物的精度值为 ±0.6‰和±1.2‰，用于 δN 和 δO 的 NaCl 溶液，±0.8‰和±1.2‰用于 NaCO 溶液。重复（城市）样品表明，NaCO 溶液对 HNO 收集的选择性明显低于 NaCl 溶液。发现尼龙过滤器可以有效地收集并保留实验室生成的 NaNO 和 NHNO 颗粒，δN 和 δO 的最大标准偏差分别为±0.3‰和±0.3‰。虽然野外重复样品的变化较大，但它们在颗粒态的 δN 和 δO 方面也表现出一致性，分别为±0.6‰和±1.3‰。用于同位素测量的特定形态 HNO 和 pNO 的野外收集的推荐方法最好利用 NaCl 溶液和尼龙过滤器。
