Peroxyacetyl nitrate persists across boundary-layer regimes and varies with transport pathway at an elevated East Asian receptor

Abstract. Peroxyacetyl nitrate (PAN) is a thermally reversible reservoir of reactive nitrogen that redistributes ozone-production potential from NO_x source regions. Its persistence at elevated East Asian receptors under interacting transport, photochemistry, and boundary-layer exchange remains poorly constrained. We investigated PAN at the summit of Mount Gaya, Korea (678 m a.s.l.), during the same spring periods in 2022 and 2023 using paired photolytic- and molybdenum-converter NO₂ measurements, direct PAN observations, ERA5 boundary-layer diagnostics, and 72 h HYSPLIT backward trajectories. The converter difference, defined as operational gas-phase NO_z^* (= NO₂,Moly − NO₂,Photo), averaged 2.12 ppbv in both campaigns and represented 57.5–58.0 % of the molybdenum-converter response. In 2023, PAN averaged 0.64 ± 0.51 ppbv, and the ratio of campaign-mean PAN to campaign-mean NO_z^* was 30.2 %. PAN/NO_z^* ratios showed no systematic enhancement under boundary-layer-decoupled conditions after temporal autocorrelation was considered. Trajectory-level median PAN was 0.66 ppbv for Continental East Asia, 0.58 ppbv for Korean Peninsula regional, and 0.35 ppbv for Marine/Background pathways, with a significant overall pathway dependence. In contrast, median PAN/NO_z^* ratios of 33.2 %, 28.2 %, and 28.5 %, respectively, did not differ significantly among pathways. PAN-rich episodes further showed that the largest PAN enhancement and the highest PAN/NO_z^* ratio occurred under different transport conditions. These observations indicate that PAN persistence at Mount Gaya reflects the combined influence of continental transport, regional photochemical processing, and vertical exchange rather than boundary-layer isolation alone, and that PAN can constitute a substantial directly measured component of converter-responsive oxidized nitrogen.