Vertical Distribution of Sources and Atmospheric Impacts of HONO in the North China Plain.

Nitrous acid (HONO) plays a significant role in tropospheric air quality as a crucial precursor of hydroxyl radicals (OH). While extensive research has focused on ground-level HONO, the sources and atmospheric implications of high-altitude HONO remain poorly understood. In this study, the Community Multiscale Air Quality (CMAQ) model was employed to explore the vertical distribution of HONO chemistry.

Oxygenated Organic Molecules over the Boundary Layer Aloft in Beijing.

Oxygenated organic molecules (OOMs) originate from both direct emissions and secondary formation via the oxidation of volatile organic compounds (VOCs) emitted from biogenic and anthropogenic sources. OOMs are suggested to play a crucial role in the nucleation and growth of newly formed particles, which in turn influence climate, health and air quality. However, OOMs and the associated nucleation and growth of aerosols in the boundary layer aloft are not considered in atmospheric chemistry models owing to limited observation data.

Changing aerosol chemistry is redefining HONO sources.

Heterogeneous reactions of NO on particulate matter have been considered an important source of HONO (Nitrous acid) in the troposphere, whereas its contribution is controversial due to the lack of uptake coefficient of NO (γ) on the surfaces of ambient particulate matter (PM). Here we investigate the the γ to form HONO and its evolution based on long-term comprehensive field observations (2019-2023) in Beijing and a random forest model with Shapley additive explanations. The γ on ambient PM is on the order of 10, decreasing markedly from 3.

Unexpected SO Photooxidation on Quantum-Sized Carbon.

Surface photochemistry of carbon quantum dots (CQD) under atmospheric conditions remains poorly understood. Here, we systematically investigate the photoreactivity of CQD in the presence of SO and reveal that CQD photoageing and its interaction with SO occur independently of O. Through a combined experimental and theoretical approach, we demonstrate that these unexpected surface reactions are driven by unique energy transfer and photocatalytic processes induced by photoexcited CQD.

Environmental catalytic city: New engine for air pollution control.

Air pollution is a major challenge to the improvement of urban environmental quality. The control of air pollution still faces severe challenges, especially in developing countries, such as ozone pollution control. Ozone is a typical secondary air pollutant, and its formation chemistry from its precursors (NO and volatile organic compounds) is highly nonlinear, which caused the emission reduction of its precursors is not always effective and therefore new assisted approaches to control of ozone pollution are needed.

Research on the influencing factors of PM in China at different spatial scales based on machine learning algorithm.

PM pollution is one of the prominent environmental issues currently faced in China, influenced by various factors and showed significant spatial differences. In this study, the Light Gradient Boosting Machine (LightGBM) model was employed in combination with SHapley Additive exPlanation (SHAP) methods to explore the key impact factors (precursor emissions, meteorological conditions, geographical features and socioeconomic factors) on average annual PM levels from 2015 to 2022 at both city and grid levels in China. The results show that incorporating pollutant concentration into the model enhances its performance, with R improving significantly from 0.

Formation of Nitrate in the Residual Layer of Beijing: Pathways Evaluation and Contributions to the Ground Level.

High concentrations of particulate matter severely degrade air quality and pose significant threats to public health. Nitrate-driven pollution has long been recognized as a primary contributor to haze formation at the ground surface in Beijing. Here, comprehensive observations of NO and related species were conducted using a unique 528 m platform in Beijing.

SO-Promoted Molecular Oxygen Activation and NO Oxidation on γ-MnO.

The activation of molecular oxygen on transition metal oxide surfaces plays a crucial role in atmospheric chemistry and heterogeneous catalysis; however, understanding the intricate mechanisms remains a challenge. In this study, we elucidate for the first time the role of sulfur dioxide (SO) in enhancing oxygen activation on manganese oxide (γ-MnO) surface, thereby facilitating the oxidation of nitric oxide (NO) to nitrogen dioxide (NO). The theoretical calculation results further demonstrate that the adsorbed SO and the formed sulfate can promote the adsorption of O and the reactivity of surface reactive oxygen species toward NO oxidation on γ-MnO (110) surface, respectively.

Unexpectedly High Levels of HO Drive Sulfate Formation over the Residual Layer in Beijing.

Hydrogen peroxide (HO) plays a key role in atmospheric chemistry, but knowledge of its variation, sources, and impact on sulfate formation remains incomplete, especially in the urban boundary layer aloft. Here, we conducted a field campaign with measurements of HO and related species at a tower-based site (∼528 m above the ground surface) of Beijing in spring of 2022. The observed hourly HO concentration reached up to 21.

A Review of Laboratory Studies on the Heterogeneous Chemistry of NO: Mechanisms and Uptake Kinetics.

NO is a significant primary atmospheric pollutant that plays a key role in atmospheric chemistry. It serves as a crucial precursor to photochemical smog, acid rain, and secondary particulate matter and is instrumental in determining the atmospheric oxidation capacity. In this review, we focus on the heterogeneous chemistry of NO, which has been demonstrated to significantly influence the sources and sinks of various nitrogen-containing species through field measurements and model simulations.

Dark NO Reduction on a Graphene Surface with Implications for Soot Aging and HONO Formation.

Soot, primarily composed of elemental carbon (EC) and organic carbon (OC), is ubiquitous in PM. In the atmosphere, the heterogeneous interaction between NO and soot is not only an important pathway driving soot aging but also of central importance to nitrous acid (HONO) formation. It is commonly believed that the surface redox reaction between reductive OC and NO dominates the night aging of soot and the conversion of NO to HONO.

Spontaneous Molecular Bromine Production in Sea-Salt Aerosols.

Bromine chemistry is responsible for the catalytic ozone destruction in the atmosphere. The heterogeneous reactions of sea-salt aerosols are the main abiotic sources of reactive bromine in the atmosphere. Here, we present a novel mechanism for the activation of bromide ions (Br) by O and HO in the absence of additional oxidants.

Insights into the Formation Mechanism of Reactive Oxygen Species in the Interface Reaction of SO on Hematite.

The interplay between sulfur and iron holds significant importance in their atmospheric cycle, yet a complete understanding of their coupling mechanism remains elusive. This investigation delves comprehensively into the evolution of reactive oxygen species (ROS) during the interfacial reactions involving sulfur dioxide (SO) and iron oxides under varying relative humidity conditions. Notably, the direct activation of water by iron oxide was observed to generate a surface hydroxyl radical (•OH).

Characteristics, sources, and health risks of volatile organic compounds in different functional regions of Shenyang.

The concentration of 56 volatile organic compounds (VOCs) in the ambient air of Shenyang was continuously monitored at four sites in 2021. The characteristics, sources, secondary pollution potential and health risks of VOCs in different functional regions of Shenyang were discussed. The results indicate that the concentration of VOCs in industrial regions was significantly higher than that in non-industrial regions, with a mean of 41.

Revealing the Contribution of Interfacial Processes to Atmospheric Oxidizing Capacity in Haze Chemistry.

The atmospheric oxidizing capacity is the most important driving force for the chemical transformation of pollutants in the atmosphere. Traditionally, the atmospheric oxidizing capacity mainly depends on the concentration of O and other gaseous oxidants. However, the atmospheric oxidizing capacity based on gas-phase oxidation cannot accurately describe the explosive growth of secondary particulate matter under complex air pollution.

Additional HONO and OH Generation from Photoexcited Phenyl Organic Nitrates in the Photoreaction of Aromatics and NO.

HONO acts as a major OH source, playing a vital role in secondary pollutant formation to deteriorate regional air quality. Strong unknown sources of daytime HONO have been widely reported, which significantly limit our understanding of radical cycling and atmospheric oxidation capacity. Here, we identify a potential daytime HONO and OH source originating from photoexcited phenyl organic nitrates formed during the photoreaction of aromatics and NO.

An Alternative Calibration Method for Measuring NO with an Iodide-Chemical Ionization Mass Spectrometer and Influencing Factors.

In this work, we developed an alternative calibration method for measuring NO with an iodide adduct mass spectrometer (I-CIMS). In this calibration method, NO is heated and then quantified based on the decrease in the amount of NO due to its reaction with the pyrolysis product (NO). This alternative calibration method was compared with the commonly used method utilizing NO analyzers equipped with a photolytic converter, which gauge NO reduction as a result of its reaction with O to quantify NO.

Photoactivation of Chlorine and Its Catalytic Role in the Formation of Sulfate Aerosols.

We present a novel mechanism for the formation of photocatalytic oxidants in deliquescent NaCl particles, which can greatly promote the multiphase photo-oxidation of SO to produce sulfate. The photoexcitation of the [Cl-HO-O] complex leads to the generation of Cl and OH radicals, which is the key reason for enhancing aqueous-phase oxidation and accelerating SO oxidation. The mass normalization rate of sulfate production from the multiphase photoreaction of SO on NaCl droplets could be estimated to be 0.

Iodine oxoacids enhance nucleation of sulfuric acid particles in the atmosphere.

The main nucleating vapor in the atmosphere is thought to be sulfuric acid (HSO), stabilized by ammonia (NH). However, in marine and polar regions, NH is generally low, and HSO is frequently found together with iodine oxoacids [HIO, i.e.

Nonlinear effect of NO concentration decrease on secondary aerosol formation in the Beijing-Tianjin-Hebei region: Evidence from smog chamber experiments and field observations.

During the COVID-19 lockdown in the Beijing-Tianjin-Hebei (BTH) region in China, large decrease in nitrogen oxides (NO) emissions, especially in the transportation sector, could not avoid the occurrence of heavy PM pollution where nitrate dominated the PM mass increase. To experimentally reveal the effect of NO control on the formation of PM secondary components (nitrate in particular), photochemical simulation experiments of mixed volatile organic compounds (VOCs) under various NO concentrations with smog chamber were performed. The proportions of gaseous precursors in the control experiment were comparable to ambient conditions typically observed in the BTH region.

Combined Smog Chamber/Oxidation Flow Reactor Study on Aging of Secondary Organic Aerosol from Photooxidation of Aromatic Hydrocarbons.

Secondary organic aerosol (SOA) is a significant component of atmospheric fine particulate matter (PM), and their physicochemical properties can be significantly changed in the aging process. In this study, we used a combination consisting of a smog chamber (SC) and oxidation flow reactor (OFR) to investigate the continuous aging process of gas-phase organic intermediates and SOA formed from the photooxidation of toluene, a typical aromatic hydrocarbon. Our results showed that as the OH exposure increased from 2.

The role of NO in Co-occurrence of O and PM pollution driven by wintertime east Asian monsoon in Hainan.

Clarifying the driving forces of O and fine particulate matter (PM) co-pollution is important to perform their synergistic control. This work investigated the co-pollution of O and PM in Hainan Province using an observation-based model and explainable machine learning. The O and PM pollution that occurs in winter is affected by the wintertime East Asian Monsoon.

Effects of SO on NHNO Photolysis: The Role of Reducibility and Acidic Products.

Nitrate photolysis is a vital process in secondary NOx release into the atmosphere. The heterogeneous oxidation of SO due to nitrate photolysis has been widely reported, while the influence of SO on nitrate photolysis has rarely been investigated. In this study, the photolysis of nitrate on different substrates was investigated in the absence and presence of SO.

The contribution of industrial emissions to ozone pollution: identified using ozone formation path tracing approach.

Wintertime meteorological conditions are usually unfavorable for ozone (O) formation due to weak solar irradiation and low temperature. Here, we observed a prominent wintertime O pollution event in Shijiazhuang (SJZ) during the Chinese New Year (CNY) in 2021. Meteorological results found that the sudden change in the air pressure field, leading to the wind changing from northwest before CNY to southwest during CNY, promotes the accumulation of air pollutants from southwest neighbor areas of SJZ and greatly inhibits the diffusion and dilution of local pollutants.

Photocatalytic Oxidation of NO on TiO : Evidence of a New Source of N O.

N O is an important intermediate in the atmospheric nitrogen cycle. Using a flow tube reactor, N O was found to be released from the TiO surface during the photocatalytic oxidation of NO , revealing a previously unreported source of N O . The rate of N O release from TiO was dependent on the initial NO concentration, relative humidity, O /N ratio, and irradiation intensity.