Insight Into the Environment Implication of Primary and Photochemical Aging Processes of Nitrogen-Containing Organic Chromophores From Residential Fuel Combustion Over Qinghai-Tibet Plateau

Abstract

The Qinghai-Tibet Plateau (TPL), crucial for the global climate, lacks a comprehensive understanding of nitrogen-containing organic compound (NOCs) emissions and their impact on light absorption and radiative forcing through atmospheric oxidation. This study examined NOCs from dung and bitumite combustion in the TPL and their atmospheric oxidation by hydroxyl (·OH) and nitrate (·NO₃) radicals using an integrated experimental and theoretical approach. Dung produced higher NOC emissions, mainly methyl types, while bitumite emitted more fused-ring NOCs. Exposure to intense solar radiation resulted in substantial photobleaching of methyl NOCs through hydroxyl (·OH) reactions, reducing the maximum molar absorption at 300–400 nm wavelengths by 76.9%–96.4%. Moreover, nitrate radical (·NO₃) oxidation maintained spectral characteristics while producing minor absorption decreases of 48.9%–58.8%. The oxidative aging of fused-ring NOCs exhibited structure-dependent responses, wherein both ·NO₃ and ·OH oxidation induced photo-enhancement effects proportional to the number of aromatic rings in the molecular structure. Oxidation generally reduced radiative forcing for methyl NOCs but enhanced it for fused-ring NOCs, particularly through ·OH reactions, which increased simple forcing efficiency at 300–400 nm by 43.7%. This study provides crucial insights into NOCs' effects on regional climate and air quality, emphasizing the need for source-specific considerations in atmospheric models for TPL's unique high-altitude environment.