Contributions of primary emissions and secondary formation to nitrated aromatic compounds in themountain background region of Southeast China

Abstract. Nitrated aromatic compounds (NACs), a major component of brown carbon (BrC), have a significant role in the atmosphere’s ability to absorb light. Despite this, the sources and major influencing variables of the mountain background atmosphere are mostly lacking. The current work is based on a thorough field investigation of NACs from fine particle samples taken in 2014 and 2015 at the peak of Mt. Wuyi (1139 meters above sea level) and includes a thorough examination of the seasonal fluctuations in their composition, sources, and significant influencing factors. As a result of the air masses traveling mostly via northern heating zones, the total abundance of nine quantifiable NACs increased significantly in the winter (3.9 ± 1.5 ng m-3) and autumn (2.1± 0.94 ng m-3), whereas it decreased in the spring (1.3 ± 0.75 ng m-3) and summer (0.97 ± 0.36 ng m-3). The most prevalent NAC species during the year was 4- nitrocatechol (25.8 %), followed by 5-nitroguaiacol (17.6 %). In addition, the majority of NACs (93 %) were influenced by coal, biomass, and petroleum combustion over the entire year, according to the results of structural equation modeling (SEM). Pollutant movement had a significant impact on the atmospheric NACs at the peak of Mt. Wuyi, especially in the winter (93.4 %) and spring (68.7 %). Long-range transport of nitration reactions was the dominant style in the transport process during the winter (33.7 %), while long-range transport of mixed sources was significant throughout the other seasons (14 %–37 %). In particular, for 4-nitrocatechol, NO2 may enhance the generation of NACs with a major impact on their compositions. Under low-NOx conditions, the formation of NACs was comparatively sensitive to NO2, suggesting that NACs would become significant in the aerosol characteristics when nitrate concentrations decreased as a result of emission reduction measures.