Multi-site non-methane hydrocarbon source apportionment and ozone insights in Southern Taiwan using positive matrix factorization

Abstract. Ozone pollution remains a persistent challenge in Taiwan's Kaoping region due to dense industrial and urban emissions. Using high-resolution, hourly observations from three Photochemical Assessment Monitoring Stations (PAMS) combined with Positive Matrix Factorization (PMF), this study resolved eight distinct sources of non-methane hydrocarbons (NMHCs), key precursors of ozone formation. The time-resolved PMF output captured source-specific temporal patterns – as shown by the acetylene factor at Linyuan (R2 = 0.99 with observations) – providing an intrinsic check on model performance and facilitating spatial interpretation of sources. Petroleum-related emissions dominate NMHC mass at all sites but are more prominent at Xiaogang, while aged air masses substantially enhance ozone pollution at downwind locations such as Linyuan and Chaozhou, underscoring the role of regional transport and atmospheric aging. Although mixed sources from vehicular and solvent emissions contributed less mass, they dominated ozone formation potential (OFP) due to higher chemical reactivity. Notably, their influence persisted even under moderate ozone conditions, indicative of a VOC-limited regime. Overall, these results emphasize that effective ozone mitigation in southern Taiwan requires coordinated control of petroleum, mobile, and solvent emissions, and demonstrate the value of multi-site, year-round, high-time-resolution NMHC measurements for constraining ozone precursors.