Primary nitrated phenol emissions from heavy-duty diesel vehicles based on real-world activity data in Hunan, China

Nitrated phenols (NPs) are important reactive and light-absorbing organic compounds in the atmosphere, but primary NP emissions from heavy-duty diesel vehicles (HDDVs) remain poorly quantified in emission inventories, particularly with respect to their total magnitude and distributions across vehicle categories, emission standards, individual compounds, time, and space. Here, we quantified primary measured NP emissions from HDDVs in Hunan Province, China, for 2025 by combining NP emission factors and compound profiles obtained from tandem filter and polyurethane foam (PUF) exhaust sampling with real-world vehicle activity data. Total NP emissions from HDDVs were estimated to be 1196.8 kg yr^-1. Emissions were highly concentrated in freight-related fleets, with container trucks, freight trucks and buses contributing 48.3, 22.9 and 17.7% of total emissions, respectively. China IV and China V vehicles dominated the inventory, together accounting for 84.1% of total emissions, reflecting the combined influence of non-negligible emission factors and high real-world activity. The compound-resolved inventory showed that 4-nitrophenol was the dominant species, contributing 334.9 kg yr^-1, followed by methyl nitrophenols and nitrocatechol-related species. Monthly emissions ranged from 76.8 kg in February to 114.4 kg in December, indicating that annual-average temporal allocation would obscure seasonal emission variation. Spatially, the five highest-emitting cities contributed 53.9% of provincial emissions, indicating pronounced city-level heterogeneity. Monte Carlo analysis yielded a 95% confidence interval of 544.7 - 2341.7 kg yr^-1 for total provincial emissions and identified emission factors as the dominant uncertainty source. These results provide a regional-scale quantitative constraint on primary diesel-derived NP emissions and identify the vehicle fleets, emission standards, compounds, periods, and locations that dominate emissions, thereby establishing a basis for evaluating the contribution and spatial relevance of diesel vehicles to atmospheric NPs.