“…Modeling studies have also shown that the lack of NOy measurements hinder a comprehensive understanding of the heterogeneous reactions (Anderson et al, 2014;Wang et al, 2017b;Chen et al, 2018). HONO, one of the NOy species, is an early morning source of OH radicals in the urban atmosphere (Brandenburger et al, 1998;Xing et al, 2019;Alicke et al, 2002;Ryan et al, 2018;Gil et al, 2020;Xue et al, 2020). Thus, there has been a steady effort to determine the atmospheric level of HONO using various methods such as a long path absorption photometer (LOPAP) (Kleffmann et al, 2006;Xue et al, 2019), chemical ionization mass spectrometry (CIMS) (Levy et al, 2014;Roberts et al, 2010), ion chromatography (IC) (VandenBoer et al, 2014;Gil et al, 2020;Ye et al, 2016;Xu et al, 2019), and quantum cascade tunable infrared laser differential absorption spectrometry (QC-TILDAS) (Lee et al, 2011;Gil et al, 2021).…”