Project No: 16201623

Title: Source, formation, and gas-particle partitioning of nitro-phenolic compounds and their environmental impacts in subtropical Hong Kong

Principal Investigator: Prof. Zhe WANG

Co-Investigator: Prof. Jianzhen YU

Abstract:

Nitro-phenolic (NP) compounds are important atmospheric pollutants attracting increasing attention due to their health risks and impacts on air quality, visibility, and climate change. NPs are emitted from various anthropogenic and biomass-burning sources, and also produced from the atmospheric oxidation of organic precursors in the presence of nitrogen oxides (NOx). Studies have mostly focused on particle-phase NPs with offline measurement and have recognized them as a major component of brown carbon aerosols affecting visibility and the Earth’s radiation balance. Recent studies with high-resolution real-time measurements have revealed many gaseous NPs in the atmosphere, as characterized by their fast generation, evolution, and transformation. The photolysis of NPs can release nitrous acid (HONO), OH radicals, and other reactive products, which greatly increase atmospheric oxidation capacity and affect atmospheric chemistry. Despite their importance, our understanding of these highly reactive and semi-volatile species is far from complete. Knowledge gaps remain regarding their atmospheric abundance, distribution, formation, and transformation mechanisms, as well as their impacts on the regional scale. Continuous and simultaneous measurement of NPs in both gas and particle phases is thus essential to obtain a quantitative understanding of their sources, fates, and environmental impacts in the atmosphere. We will characterize the NPs in urban environments of Hong Kong by combining ambient observation, in-situ and laboratory experiments, and photochemical box model analysis. Ambient measurements will be conducted using state-of-the-art instruments to investigate the abundance, distribution, and origins of key NPs at the molecular level. We will also perform oxidation experiments with ambient and lab-prepared precursors to characterize the formation mechanism and yields of NPs under various conditions. Controlled experiments will be conducted to determine the gas-particle partitioning coefficients, the photolysis rate of different NPs, and the subsequent formation yield of HONO and other reactive products. Lastly, observation-based photochemical box model simulation will be used for comprehensive budget analysis to quantify the formation and loss pathways of NPs, and to evaluate their impacts on the atmospheric radicals budget and oxidative capacity, as well as O3 and SOA formation. This proposed project will improve our understanding of the sources and fates of NPs, particularly with respect to their formation from anthropogenic precursors in urban environments, and their roles in photochemical air pollution. The results will provide valuable information to policymakers to develop effective control measures on critical organic precursors to mitigate photochemical O3 and haze pollution in urbanized subtropical regions.