“…3. Additionally, a number of analyses of field studies have used the NO x + 110 ratios (or its 46/30 UMR equivalent) to support qualitative or semi-quantitative statements about the presence (or low contribution) of pRONO 2 (Setyan et al, 2012;Brown et al, 2013;Xu et al, 2016;Schneider et al, 2017;Bottenus et al, 2018) or to quantify pRONO 2 (Fry et al, 2013(Fry et al, , 2018Ayres et al, 2015;Kostenidou et al, 2015;Xu et al, 2015aXu et al, , 2021Fisher et al, 2016;Kiendler-Scharr et al, 2016;Lee et al, 2016Lee et al, , 2019Nault et al, 2016;Zhou et al, 2016;Zhu et al, 2016Zhu et al, , 2021Florou et al, 2017;115 Palm et al, 2017;Brito et al, 2018;de Sá et al, 2018de Sá et al, , 2019Reyes-Villegas et al, 2018;Schulz et al, 2018;Avery et al, 2019;Dai et al, 2019;Huang et al, 2019aHuang et al, , 2019bYu et al, 2019;Chen et al, 2020. Yu et al (2019) also used the particle size dependence of the 46/30 ratio to investigate particle size and temporal (diurnal and seasonal) trends in pRONO 2 .…”