Clouds and fogs are vital in atmospheric chemistry, as they facilitate multiphase reactions.
Fog as groundlevel clouds offer a unique opportunity for direct observation. We explored radiation fogs in the North China Plain using an advanced aerosol-fog sampling system to measure the chemical and physical properties of both inactivated interstitial aerosols and activated fog droplet residues. Results revealed efficient nitrate formation primarily occurring on fog interstitial aerosols through NO2 and N2O5 hydrolysis, rather than within fog droplets. Our results highlight the need for further research into the chemistry of cloud and fog interstitial aerosols and their inclusion in atmospheric chemistry models.

HONO represents a key nitrogen species in the troposphere because its photolysis produced OH radicals. However HONO daytime sources remain controversial. In this study we perform Coated Wall Flow Tube (CWFT) experiments and model simulations to investigate the role of Fe(III)-carboxylate photochemistry in multiphase processes that convert nitrogen dioxide (NO2) into HONO. Our results indicate a key role of Fe(II) coming from Fe(III)-carboxylate photoreduction, highlighting the importance of Fe(III) complexes photochemistry in affecting the atmospheric nitrogen cycle.

Secondary organic aerosol (SOA) is important for air quality and climate. When SOA mixes with particles containing transition metals like Fe, metal-organic complexes can form, driving photochemical aging. We studied the photochemistry of α-pinene SOA formed on Fe-containing seed particles, at varying relative humidities (RH). Chemical morphology and photochemical reduction of single particles were analyzed by spectro-microscopy. SOA chemical composition and functionality varied with RH. Furthermore, Fe in SOA formed at high RH was readily photochemically reduced upon exposure to UV light, contrary to SOA formed at low RH. Demonstrating SOA formation conditions affect both chemical composition and photochemical aging.

In the field of atmospheric aqueous aerosols, this study aims to investigate how black carbon interacts with the multiphase chemistry of atmospheric phenols. the reaction taken into consideration is the nitration of catechol, carried out in an acidic sodium nitrite solution, in the dark, with insoluble black carbon nanoparticles. Main product of this reaction is the harmful 4-nitrocatechol, jointly with other secondary compounds. This study, due to the evidences confirming the partecipant role of black carbons in the reaction, indicates that it can also influence atmospheric chemistry with further impacts on the ecosystem, climate and human health.

We present the kinetic multilayer meta model (KM-MEMO), an automatic computer code generator and framework for describing chemical reaction kinetics in multiphase systems. KM-MEMO autogenerates Matlab code for models like KM-SUB and KM-GAP, allowing users to customize system geometry and chemical mechanisms without coding. The flux-based kinetic models explicitly resolve mass transport and chemical reactions across phases. Applications include modeling secondary organic aerosol formation, where the model aids in understanding diffusion limitations to evaporation, and the health impacts of air pollution, by quantifying oxidative stress from PM2.5 and oxidant gases in the respiratory tract.

Understanding secondary aerosol formation from vehicle emissions is crucial for mitigating climate change and air pollution. This study investigates secondary aerosol precursors from gasoline and diesel vehicles using different fuel blends. Emissions, including hydrocarbons, NOx, and PM, were measured during a WLTC. Simulated atmospheric aging in an oxidation flow reactor revealed that gasoline vehicles, particularly during cold starts, produce more secondary aerosol than diesel vehicles due to higher aromatic hydrocarbon emissions. Diesel vehicles demonstrated lower secondary aerosol formation. These findings highlight the impact of fuel composition and technologies on SA production, emphasizing the need for optimized strategies to reduce emissions.