Nitrogen Isotope Differences between Major Atmospheric NO_y Species: Implications for Transformation and Deposition Processes

Abstract

Nitrogen isotopes (δ 15 N) can trace sources of major inorganic NO y species (here referring to nitrogen dioxide (NO 2 ), nitric acid (HNO 3 ), and nitrate (NO 3 − )) in the atmosphere. However, δ 15 N variations during transformation and deposition processes of NO y species remain poorly understood. Here, we dissected δ 15 N differences between NO 2 , HNO 3 , particulate NO 3 − , and precipitation NO 3 − by converging observations of their concentrations and δ 15 N from literature sources. δ 15 N values of HNO 3 were higher by 6.9 ± 4.6‰ than those of NO 2 , indicating that the hydroxyl radical pathway dominated the HNO 3 formation. δ 15 N values of particulate NO 3 − were higher by 4.9 ± 4.2‰ than those of HNO 3 , indicating HNO 3 as a main precursor of particulate NO 3 − . δ 15 N values of precipitation NO 3 − were lower than those of HNO 3 (by 2.8 ± 3.3‰) and particulate NO 3 − (by 7.5 ± 3.5‰) but higher than those of NO 2 (by 5.1 ± 4.5‰). Relative contributions of NO 2 , HNO 3 , and particulate NO 3 − to precipitation NO 3 − were estimated as 45 ± 10%, 32 ± 5%, and 23 ± 7%, respectively, which differed from their fractions in ambient atmosphere (57 ± 14%, 14 ± 8%, and 29 ± 11%, respectively). This revealed NO 2 as an important precursor of precipitation NO 3 − and a preferential scavenger of HNO 3 by precipitation. This work is beneficial for more accurate evaluations on sources and processes of atmospheric NO y pollutants.

Significant Latitudinal Gradient of Nitrate Production in the Marine Atmospheric Boundary Layer of the Northern Hemisphere

“…It is reported that non‐zero sea surface nitrite concentrations are required for RONO 2 formation to occur (Dahl & Saltzman, 2008; Dahl et al., 2012). Seawater nitrite concentrations along the cruise path were not measured in this study, but surface ocean nitrite has been reported to be approximately 0.5–2 μM in Region A (Chen et al., 2021; Hsieh et al., 2010; Liu, Ning, et al., 2020; Liu, Yin, and Song, 2020), 0.6–1.3 μM in Region B (Buchwald et al., 2015; Michoud et al., 2014; Mordy et al., 2010), and much lower in Region C (about 0.01–0.2 μM; Christman et al., 2011; Randall et al., 2012). Therefore, ocean RONO 2 emissions may be a non‐negligible source of atmospheric NO 3 − along the cruise path.…”

Important contributions of non-fossil fuel nitrogen oxides emissions

“…It has the potential to provide reliable estimations of source contributions because the isotope effect (i.e., 15 ∆ i-NO x →w-NO3− values in this study), the variability in δ 15 N values of both sources (i.e., δ 15 N values of NO x from S1–S4 in this study), and the mixture (i.e., δ 15 N w-NO3− values in this study) 45 , 46 are considered. The SIAR model has been widely used to quantify the relative contributions of multiple NO x emission sources to p-NO 3 − and w-NO 3 − 26 , 27 , 31 , 47 . In each run of the SIAR model, the mean ± SD of δ 15 N NO x values (Supplementary Fig.…”

“…However, precipitation can scavenge both the ambient NO 2 and the oxidized NO 2 (i.e., HNO 3 and p-NO 3 − ) (Supplementary Fig. 1 ) 31 . Therefore, we can reconstruct the corresponding δ 15 N i-NO x values of the observed δ 15 N w-NO3− values (Supplementary Figs.…”

Oxidation pathways and emission sources of atmospheric particulate nitrate in Seoul: based on δ<sup>15</sup>N and Δ <sup>17</sup>O of PM<sub>2.5</sub>

“…In this study, the Δ 17 O-O3* of 37.5‰ ± 2.2‰ was averaged from previous observations, corresponding to Δ 17 O-bulk O3 of 25‰ (Vicars et al, 2012;Vicars and Savarino, 2014). Our mean Δ 17 O-O3* of 37.5‰ was 2.8‰ higher and 1.5‰ lower than what was used in (Liu et al, 2020;Wang et al, 2019b) and (He et al, , 2020 for urban Beijing and Shanghai, respectively. When sensitivity test was conducted for the proportional contribution of the three oxidation pathways, a 2.8‰ change in Δ 17 O-O3* value caused 1.6‰, 2.1‰, and 2.5‰ change in the endmember for (1), (2), and (3) pathway, respectively.…”