Atmospheric Aerosol Formation Research Articles

Research Progress on Heterogeneous Reactions of Pollutant Gases on the Surface of Atmospheric Mineral Particulate Matter in China

Haze is the phenomenon of visibility degradation caused by extinction effects related to the physicochemical properties of atmospheric particulate matter (APM). Atmosphere heterogeneous reactions can alter the physicochemical properties of APM. Therefore, it is important to understand the atmospheric heterogeneous reactions of APM in order to reveal the cause of haze. Herein, the current situation, developmental trend, source, and composition of APM pollution in China are reviewed. Additionally, we introduce the reaction characteristics and key chemical processes of common inorganic, organic, and mixed pollutant gases on the surface of mineral particles. The effects of mineral particulate matter on aggregation, regulation, and catalysis in the formation of atmospheric aerosols and the synergistic reaction mechanism of SO2, NO2, O3, and VOCs on the surfaces of different mineral particles are summarized. The problems existing in the current research on heterogeneous reactions on the surfaces of mineral particles are also evaluated. This paper aims to gain a deep understanding of the mechanism of mineral particulate matter promoting the formation of secondary aerosols and attempts to provide theoretical support for effective haze control.

Greenland Ice Sheet Surfaces Colonized by Microbial Communities Emit Volatile Organic Compounds.

Volatile organic compounds (VOCs) are emitted by organisms for a range of physiological and ecological reasons. They play an important role in biosphere–atmosphere interactions and contribute to the formation of atmospheric secondary aerosols. The Greenland ice sheet is home to a variety of microbial communities, including highly abundant glacier ice algae, yet nothing is known about the VOCs emitted by glacial communities. For the first time, we present VOC emissions from supraglacial habitats colonized by active microbial communities on the southern Greenland ice sheet during July 2020. Emissions of C5–C30 compounds from bare ice, cryoconite holes, and red snow were collected using a push–pull chamber active sampling system. A total of 92 compounds were detected, yielding mean total VOC emission rates of 3.97 ± 0.70 μg m–2 h–1 from bare ice surfaces (n = 31), 1.63 ± 0.13 μg m–2 h–1 from cryoconite holes (n = 4), and 0.92 ± 0.08 μg m–2 h–1 from red snow (n = 2). No correlations were found between VOC emissions and ice surface algal counts, but a weak positive correlation (r = 0.43, p = 0.015, n = 31) between VOC emission rates from bare ice surfaces and incoming shortwave radiation was found. We propose that this may be due to the stress that high solar irradiance causes in bare ice microbial communities. Acetophenone, benzaldehyde, and phenylmaleic anhydride, all of which have reported antifungal activity, accounted for 51.1 ± 11.7% of emissions from bare ice surfaces, indicating a potential defense strategy against fungal infections. Greenland ice sheet microbial habitats are, hence, potential sources of VOCs that may play a role in supraglacial microbial interactions, as well as local atmospheric chemistry, and merit future research efforts.

Combined effects of high relative humidity and ultraviolet irradiation: Enhancing the production of gaseous NO2 from the photolysis of NH4NO3

Free radicals and nitrogen-containing species produced by nitrate photolysis can affect various atmospheric chemical processes, and thereby the photochemical behavior of atmospheric nitrate aerosols has been attracting much attention. However, the photolysis mechanism of NH4NO3 and its products under different atmospheric conditions remain unclear. In this study, the effects of relative humidity (RH), pH, NH3, ultraviolet (UV) light intensity and halogen ions (Cl−, Br− and I−) on the photolysis of particulate NH4NO3 have been investigated through a flow tube reactor. The results show that RH can significantly enhance the production of gaseous NO2 from the photolysis of NH4NO3 when RH is higher than its deliquescence RH, but almost no NO2 is generated under dry conditions. Under high RH and UV light, the main product of NH4NO3 photolysis is NO2, rather than NO and HONO, and another main species HNO3 which mainly comes from the hydrolysis of product NO2 in the gas path was detected. Almost no NO2 and HNO3 are produced under high RH without UV light or low RH with UV light, showing the combined effect of high RH and UV irradiation on the photolysis of NH4NO3. In addition, under high RH, the lower the pH and the stronger the light intensity, the higher the NO2 production. Furthermore, surprising yields of NO and HONO are detected in the presence of halogen ions, especially in the presence of I−, indicating the important role of halogen ion in the nitrate photolysis. These results provide new insights into the photolysis of atmospheric nitrate aerosols, and may contribute to elucidating the formation and migration of atmospheric nitrate aerosols and the potential mechanisms of the occurrence and evolution of atmospheric pollution and ozone pollution.

Chemical identification and quantification of volatile organic compounds emitted by sewage sludge

The recycling of organic waste products (e.g. sewage sludge, SS) is currently being promoted as a substitute for mineral fertilizers for agricultural lands. The spreading of SS allows the recycling of the nutrients and organic matter it contains. SS contains various pollutants such as volatile organic compounds (VOCs) that adversely affect the ecosystem and human health through ozone production and serve as critical precursors of atmospheric secondary organic aerosols. There are very few studies quantifying the gaseous compounds emitted from SS, and those studies primarily address their odorant properties for identifying suitable odour abatement techniques. There is an urgent need for more comprehensive quantitative information on VOCs emitted from SS as aerosol precursors. In this context, an experimental study was performed on SS samples taken from a wastewater treatment plant located in France. Undigested SS (UDSS), digested SS (DSS) and SS with 30% and 60% dryness were collected from different stages of treatment sequence and analyzed using atmospheric simulation chambers coupled to proton-transfer-reaction quadrupole ion-guide time-of-flight mass spectrometer. Our study revealed that SS samples emitted a large spectrum of VOCs. 380 compounds were detected, quantified and classified into different chemical groups. The VOC emissions increased with the increase in the dryness of the sample; the highest being in SS 60%, followed by SS 30%, UDSS and DSS. OVOCs were dominant in SS 60%. The statistical analysis showed that the anaerobic digestion and the dewatering to 60% of dryness decreased the emissions of sulphuric compounds. Aromatic compounds and indoles (e.g. skatole) were emitted significantly from the UDSS. Some of these VOCs can serve as precursor gases for atmospheric aerosol formation. The experimental dataset obtained in this study provides an accurate inventory reference for the VOC emissions from SS samples and shows the impacts of the treatment on emission characteristics of VOCs.

Detection of Sulfur Dioxide by Broadband Cavity-Enhanced Absorption Spectroscopy (BBCEAS).

Sulfur dioxide (SO2) is an important precursor for the formation of atmospheric sulfate aerosol and acid rain. We present an instrument using Broadband Cavity-Enhanced Absorption Spectroscopy (BBCEAS) for the measurement of SO2 with a minimum limit of detection of 0.75 ppbv (3-) using the spectral range 305.5–312 nm and an averaging time of 5 min. The instrument consists of high-reflectivity mirrors (0.9985 at 310 nm) and a deep UV light source (Light Emitting Diode). The effective absorption path length of the instrument is 610 m with a 0.966 m base length. Published reference absorption cross sections were used to fit and retrieve the SO2 concentrations and were compared to fluorescence standard measurements for SO2. The comparison was well correlated, R2 = 0.9998 with a correlation slope of 1.04. Interferences for fluorescence measurements were tested and the BBCEAS showed no interference, while ambient measurements responded similarly to standard measurement techniques.

Tropical and Boreal Forest – Atmosphere Interactions: A Review

This review presents how the boreal and the tropical forests affect the atmosphere, its chemical composition, its function, and further how that affects the climate and, in return, the ecosystems through feedback processes. Observations from key tower sites standing out due to their long-term comprehensive observations: The Amazon Tall Tower Observatory in Central Amazonia, the Zotino Tall Tower Observatory in Siberia, and the Station to Measure Ecosystem-Atmosphere Relations at Hyytiäla in Finland. The review is complemented by short-term observations from networks and large experiments. The review discusses atmospheric chemistry observations, aerosol formation and processing, physiochemical aerosol, and cloud condensation nuclei properties and finds surprising similarities and important differences in the two ecosystems. The aerosol concentrations and chemistry are similar, particularly concerning the main chemical components, both dominated by an organic fraction, while the boreal ecosystem has generally higher concentrations of inorganics, due to higher influence of long-range transported air pollution. The emissions of biogenic volatile organic compounds are dominated by isoprene and monoterpene in the tropical and boreal regions, respectively, being the main precursors of the organic aerosol fraction. Observations and modeling studies show that climate change and deforestation affect the ecosystems such that the carbon and hydrological cycles in Amazonia are changing to carbon neutrality and affect precipitation downwind. In Africa, the tropical forests are so far maintaining their carbon sink. It is urgent to better understand the interaction between these major ecosystems, the atmosphere, and climate, which calls for more observation sites, providing long-term data on water, carbon, and other biogeochemical cycles. This is essential in finding a sustainable balance between forest preservation and reforestation versus a potential increase in food production and biofuels, which are critical in maintaining ecosystem services and global climate stability. Reducing global warming and deforestation is vital for tropical forests.

Measurement report: Long-term measurements of aerosol precursor concentrations in the Finnish subarctic boreal forest

Abstract. Aerosol particles form in the atmosphere via the clustering of certain atmospheric vapors. After growing into larger particles by the condensation of low-volatility gases, they can affect the Earth's climate by scattering light and acting as cloud condensation nuclei (CCN). Observations of low-volatility aerosol precursor gases have been reported around the world, but longer-term measurement series and any Arctic data sets showing seasonal variation are close to nonexistent. Here, we present ∼7 months of aerosol precursor gas measurements performed with a nitrate-based chemical ionization atmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometer. We deployed our measurements ∼150 km north of the Arctic Circle at the SMEAR I (Station for Measuring Ecosystem–Atmosphere Relations) continental Finnish subarctic field station, located in the Värriö strict nature reserve. We report concentration measurements of the most common compounds related to new particle formation (NPF): sulfuric acid (SA), methane sulfonic acid (MSA), iodic acid (IA) and the total concentration of highly oxygenated organic molecules (HOMs). At this remote measurement site, SA originates from both anthropogenic and biological sources and has a clear diurnal cycle but no significant seasonal variation. MSA shows a more distinct seasonal cycle, with concentrations peaking in the summer. Of the measured compounds, IA concentrations are the most stable throughout the measurement period, except in April during which time the concentration of IA is significantly higher than during the rest of the year. Otherwise, IA has almost identical daily maximum concentrations in spring, summer and autumn, and on NPF event or non-event days. HOMs are abundant during the summer months and low in the autumn months. Due to their low autumn concentrations and high correlation with ambient air temperature, we suggest that most HOMs are products of biogenic emissions, most probably monoterpene oxidation products. NPF events at SMEAR I happen under relatively low-temperature (1–8 ∘C) conditions, with a fast temperature rise in the early morning hours as well as lower and decreasing relative humidity (RH, 55 % vs. 80 %) during NPF days compared with non-event days. NPF days have clearly higher global irradiance values (∼450 m−2 vs. ∼200 m−2) and about 10 ppbv higher ozone concentrations than non-event days. During NPF days, we have, on average, higher SA concentrations, peaking at noon; higher MSA concentrations in the afternoon; and slightly higher IA concentration than during non-event days. In summary, these are the first long-term measurements of aerosol-forming vapors from SMEAR I in the subarctic region, and the results of this work will help develop an understanding of atmospheric chemical processes and aerosol formation in the rapidly changing Arctic.

Effect of Diesel Soot on the Heterogeneous Reaction of NO2 on the Surface of γ-Al2O3

Soot and aged soot are often found to be mixed with atmospheric particles, which inevitably affect various atmospheric heterogeneous reactions and secondary aerosol formation. Previous studies have investigated the heterogeneous reaction of NO2 with different types of soot, but there are few studies on the heterogeneous reaction of NO2 with mixtures containing diesel soot (DS) or aged DS and mineral dust particles. In this study, the effects of DS and aged DS on the heterogeneous reaction of NO2 on the surface of γ-Al2O3 were investigated via in-situ diffuse reflectance infrared Fourier transform spectrometry (DRIFTS). The results showed that the DS or DS n-hexane extract significantly inhibited the formation of nitrate on γ-Al2O3 particles and promoted the formation of nitrite. At 58% RH, with the increase of DS or DS n-hexane extract loading amount, the effect of DS or DS n-hexane extract on the formation of nitrate changed from promotion to inhibition, but DS or DS n-hexane extract always promoted the formation of nitrite. The results also showed that light was conducive to the formation of nitrate on the DS-γ-Al2O3 or DS-n-hexane extract-γ-Al2O3 particles. Furthermore, the influence of soot aging on the heterogeneous reaction of NO2 was investigated under light and no light. In the dark, O3-aged DS-γ-Al2O3 or O3-aged DS-n-hexane extract-γ-Al2O3 firstly inhibited the formation of nitrate on the mixed particles and then promoted it, while the effect of aged DS on nitrite formation was complex. Under light, the O3-aged DS-γ-Al2O3 firstly promoted the formation of nitrate on the mixed particles and then inhibited it, while the O3-aged DS-n-hexane extract-γ-Al2O3 promoted the formation of nitrate on the mixed particles. Our results further showed that the production of nitrate on the O3-aged particles under light or no light was greater than that of the UV-nitrate-aged particles. This study is helpful to deeply understand the atmospheric chemical behavior of soot and the heterogeneous conversion of atmospheric NO2.

Unexpected High Contribution of Residential Biomass Burning to Non‐Methane Organic Gases (NMOGs) in the Yangtze River Delta Region of China

AbstractResidential biomass burning (BB) plays an important role in the generation of household energy in rural China and can contribute to the degradation of regional air quality. Here, unexpectedly strong residential BB emissions were identified during the EXPeriment on the eLucidation of the atmospheric Oxidation capacity and aerosol foRmation, and their Effects in Yangtze River Delta (YRD) campaign in the rural area of the Eastern China based on the early summertime measurements of non‐methane organic gases (NMOGs) by a Proton Transfer Reaction‐Quadruple Time‐of‐Flight Mass Spectrometer. These widespread and long‐lasting residential BB emissions feature high levels of acetonitrile, oxygenated‐aromatics, and naphthalene, and are independent of the characteristic emissions from the open field BB but relate to miscellaneous fuels burning such as combustible wastes. The positive matrix factorization approach was applied to quantitatively appoint sources and understand the role of residential BB on OH reactivity (LOH) and secondary organic aerosols formation potential (SOAP) in the rural atmosphere of China. We find that residential BB accounts for 24.0% ± 6.4% of all NMOG mixing ratios, compared to 40.1% ± 7.7% of urban emissions. The contribution of these two sources to the total calculated LOH (23.2% ± 6.2% from BB and 26.4% ± 5.1% from urban) and SOAP (22.0% ± 7.5% from BB and 23.2% ± 6.7% from urban) are comparable during normal days. In addition, biogenic emissions and sporadic field BB are also important sources of NMOGs in the YRD region during the harvest season. This study highlights the critical importance of residential BB emissions in the Eastern China, which were unaccounted for by the past air pollution regulations.

Computational Investigation of the Formation of Peroxide (ROOR) Accretion Products in the OH- and NO3-Initiated Oxidation of α-Pinene.

The formation of accretion products (“dimers”) from recombination reactions of peroxyl radicals (RO2) is a key step in the gas-phase generation of low-volatility vapors, leading to atmospheric aerosol particles. We have recently demonstrated that this recombination reaction very likely proceeds via an intermediate complex of two alkoxy radicals (RO···OR′) and that the accretion product pathway involves an intersystem crossing (ISC) of this complex from the triplet to the singlet surface. However, ISC rates have hitherto not been computed for large and chemically complex RO···OR′ systems actually relevant to atmospheric aerosol formation. Here, we carry out systematic conformational sampling and ISC rate calculations on 3(RO···OR′) clusters formed in the recombination reactions of different diastereomers of the first-generation peroxyl radicals originating in both OH- and NO3-initiated reactions of α-pinene, a key biogenic hydrocarbon for atmospheric aerosol formation. While we find large differences between the ISC rates of different diastereomer pairs, all systems have ISC rates of at least 106 s–1, and many have rates exceeding 1010 s–1. Especially the latter value demonstrates that accretion product formation via the suggested pathway is a competitive process also for α-pinene-derived RO2 and likely explains the experimentally observed gas-phase formation of C20 compounds in α-pinene oxidation.

Anthropogenic Volatile Organic Compound (AVOC) Autoxidation as a Source of Highly Oxygenated Organic Molecules (HOM).

Gas-phase hydrocarbon autoxidation is a rapid pathway for the production of in situ aerosol precursor compounds. It is a highway to molecular growth and lowering of vapor pressure, and it produces hydrogen-bonding functional groups that allow a molecule to bind into a substrate. It is the crucial process in the formation and growth of atmospheric secondary organic aerosol (SOA). Recently, the rapid gas-phase autoxidation of several volatile organic compounds (VOC) has been shown to yield highly oxygenated organic molecules (HOM). Most of the details on HOM formation have been obtained from biogenic monoterpenes and their surrogates, with cyclic structures and double bonds both found to strongly facilitate HOM formation, especially in ozonolysis reactions. Similar structural features in common aromatic compounds have been observed to facilitate high HOM formation yields, despite the lack of appreciable O3 reaction rates. Similarly, the recently observed autoxidation and subsequent HOM formation in the oxidation of saturated hydrocarbons cannot be initiated by O3 and require different mechanistic steps for initiating and propagating the autoxidation sequence. This Perspective reflects on these recent findings in the context of the direct aerosol precursor formation in urban atmospheres.

Vibrational Spectra of Atmospherically Relevant Hydrogen-Bonded MSA···(H2SO4)n (n = 1–3) Clusters

Methanesulfonic acid (CH3SO3H), also known as MSA, has been found to be capable of forming a strong hydrogen-bonded interaction with sulfuric acid (H2SO4) under ambient conditions. The energetic stability of the MSA···H2SO4 clusters increases with decreasing temperature at higher altitudes in the troposphere, which is relevant in the context of atmospheric aerosol formation. We have performed, in the present work, a detailed and systematic quantum-chemical calculation with high-level density functional theory to characterize the hydrogen bond formation in the binary MSA···H2SO4, ternary MSA···(H2SO4)2, and quaternary MSA···(H2SO4)3 clusters. The five different conformations of MSA···(H2SO4)2 and six conformations of MSA···(H2SO4)3, considered in the present work for the spectroscopic analysis, have been taken from our previous work [J. Phys. Chem. A. 2020, 124, 11072-11085]. The hydrogen bonds were analyzed on the basis of infrared vibrational frequencies of different O-H stretching modes and quantum theory of atoms in molecules (QTAIM). A strong positive correlation has been observed between the red shift of the OH groups in MSA and H2SO4 and the corresponding O-H elongation as a result of hydrogen bond formation. Topological analysis employing QTAIM shows that most of the charge density and the Laplacian values at bond critical points (BCPs) of the hydrogen bonds of the MSA···(H2SO4)n (n = 1-3) complexes fall within the standard hydrogen-bond criteria. However, those outside these criteria fall in the category of a very strong hydrogen bond with a hydrogen bond length as low as 1.41 Å and an O-H bond elongation as high as 0.096 Å. In general, the charge densities of the BCPs located on hydrogen bonds increase as the hydrogen-bond lengths decrease. Proportionately, a larger number of hydrogen bonds in ternary MSA···(H2SO4)2 demonstrate a partial covalent character when compared with the quaternary clusters.

Investigation of the Relations between Biogenic and Anthropogenic Sources of Organic Atmospheric Aerosol under Conditions of Restrictions Due to the Coronavirus Pandemic

—The effect of restrictions caused by the COVID-19 pandemic in Novosibirsk in spring 2020 on the composition of trace atmospheric gases and organic aerosol in the air of Novosibirsk Akademgorodok is investigated. The concentrations of aldehydes (formaldehyde, acetaldehyde, benzaldehyde, acrolein, and substituted aromatic aldehydes), the corresponding carboxylic acids, and peroxy compounds were studied before and after the adoption of restrictions, prior to the start of growing season, that is, with the minimal emission of biogenic compounds into the atmosphere. Differences in diurnal variations and the composition of hydroperoxides are revealed on a background of weakening anthropogenic sources. The role of hydroperoxides in gas-to-particle conversion is shown. In parallel, the concentrations of nanometer-sized aerosol particles were measured, and differences in their chemical composition were analyzed. To explain the observed changes in the composition of organic aerosol, the stages formation of condensable products was numerically simulated. A sharp decrease in the strength of anthropogenic sources allowed us to reveal and characterize the contribution from biogenic sources to the formation of organic atmospheric aerosol and to describe this process.

Aerosol formation in the filtered atmospheric air and regularities of their evolution

Presented is the study of atmospheric aerosol particle formation and evolution processes arising in filtered atmospheric air in complete darkness. Studies were carried out in the Large Aerosol Chamber (LAC) of RPA «Typhoon» with 3200 m3 volume under conditions close to natural atmospheric ones. The large volume of the chamber and its design features make it possible to exclude the influence of boundary conditions as well as any additional pollution sources from the chamber walls and from the equipment inside the LAC on the processes under study. We observe the formation of nanoparticles apparently due to gas-to-particle conversion in the absence of UV radiation. We investigate these newly formed particle growth regularities from 15 nm size to cloud condensation nuclei characteristic sizes under controlled conditions. The observed evolution regularities of the newly formed due to gas-to-particle conversion aerosol spectra can significantly contribute to the understanding of atmospheric aerosol formation processes responsible for cloudiness and precipitation.

ChemDyME: Kinetically Steered, Automated Mechanism Generation through Combined Molecular Dynamics and Master Equation Calculations.

In many scientific fields, there is an interest in understanding the way in which chemical networks evolve. The chemical networks which researchers focus upon have become increasingly complex, and this has motivated the development of automated methods for exploring chemical reactivity or conformational change in a "black-box" manner, harnessing modern computing resources to automate mechanism discovery. In this work, we present a new approach to automated mechanism generation which couples molecular dynamics and statistical rate theory to automatically find kinetically important reactions and then solve the time evolution of the species in the evolving network. The key to this chemical network mapping through combined dynamics and ME simulation approach is the concept of "kinetic convergence", whereby the search for new reactions is constrained to those species which are kinetically favorable at the conditions of interest. We demonstrate the capability of the new approach for two systems, a well-studied combustion system and a multiple oxygen addition system relevant to atmospheric aerosol formation.

Aqueous phase oxidation of bisulfite influenced by nitrate and its photolysis

Nitrate aerosol is ubiquitous in the atmosphere. Nitrate in the particulate and aqueous phase can affect various atmospheric chemical processes through its hygroscopicity and photolysis. The impacts of nitrate photolysis on the heterogeneous oxidation of SO2 have been attracting attention. However, the influence of nitrate on heterogeneous aqueous phase formation of atmospheric sulfate aerosol is still not very clear. In this study, the effects of nitrate on aqueous phase oxidation of bisulfite under different conditions were investigated. Results show that nitrate photolysis can promote the oxidation of bisulfite to sulfate, especially in the presence of O2. It is found that pH plays a significant role in the reaction, and ammonium sulfate has significant impacts on the enhancement of aqueous phase sulfate production through regulating the pH of solution. An apparent synergism is found among halogen chemistry, nitrate and its photochemistry and S (IV) aqueous oxidation, especially the oxidation of halide ions by nitrate and its photolysis and by the intermediate products produced by the free radical chain oxidation of S (IV) in acidic solution, leading to the coupling of the redox cycle of halogen with the oxidation of bisulfite, which promotes the continuous aqueous oxidation of bisulfite and the formation of sulfate. In addition, the role of nitrate itself in the aqueous phase oxidation of bisulfite is revealed. These results provide a new insight into the heterogeneous aqueous phase oxidation pathways and mechanisms of SO2 in cloud and fog droplets and haze particles.

Competitive formation of HSO4- and HSO5- from ion-induced SO2 oxidation: Implication in atmospheric aerosol formation

This study presents a theoretical investigation of the ion-induced SO2 oxidation by the hydroxyl (OH) and hydroperoxyl (HO2) radicals. Initiated by the superoxide ion (O2-), the reaction with HO2 to form the SO5- and HSO4− ions from two different mechanisms is prevented by high energy barriers, 30.20 and 33.42 kcal mol−1, respectively, whereas the reaction with OH to form HSO5- is highly exergonic and takes place through a barrierless process. The latter reaction, hereby, not only highlights the formation mechanism of the HSO5- ion in the gas-phase, but closes a mechanism for SO2 oxidation initiated by O2-. Giving the suspected role of HSO5- to drive aerosol formation besides HSO4- that was brought up in earlier studies, we calculated the formation energies and the thermodynamics of its clustering with 1–3 sulfuric acid molecules with and without one ammonia molecule. The results showed that the formation of HSO5--based clusters is highly exergonic and that they are more stabilized by ammonia than HSO4--based clusters in the cluster size range considered. Assuming thermal equilibrium, the abundance of the largest HSO5--containing cluster, namely NH3⋅(H2SO4)3⋅HSO5−, is determined to be higher than that of the corresponding HSO4--containing cluster at ambient conditions, in agreement with a previous experimental result. This indicates the important role the NH3⋅(H2SO4)3⋅HSO5− cluster might play in the early stages of aerosol formation, and highlights the necessity to consider larger HSO5− – sulfuric acid – bases clusters not only to clarify their implication in the mechanism of atmospheric particle formation but also to quantify their effect on aerosol formation rates.

Quantifying the impacts of inter-city transport on air quality in the Yangtze River Delta urban agglomeration, China: Implications for regional cooperative controls of PM2.5 and O3.

The Yangtze River Delta (YRD) urban agglomeration is one of the most developed regions in China. During recent decades, this region has experienced severe regional haze and photochemical smog pollution problems. In this study, we used a source-oriented chemical transport model to quantitatively estimate the effects of inter-city transport on fine particulate matter (PM2.5) and ozone (O3) among the 41 cities in the YRD urban agglomeration during the EXPLORE-YRD (EXPeriment on the eLucidation of the atmospheric Oxidation capacity and aerosol foRmation, and their Effects in the Yangtze River Delta) campaign (May 17 to June 17, 2018). The results show that inter-city transport is very significant in the YRD region. On average, the emissions from the local city, the other YRD cities, and the regions outside of the YRD contribute 25.3%, 49.9%, and 24.8% to the PM2.5, respectively, and they contribute 33.7%, 46.8%, and 19.5% of the non-background O3, respectively. On PM2.5 or O3 pollution days, the transport contribution from the non-local YRD cities becomes much more important, while the local emissions and the transport from non-YRD emissions become less important. The results also suggest that the cities within a distance of 184km and 94km contribute 60% of the PM2.5 and O3, respectively. Therefore, we recommend that regional cooperative control programs in the YRD consider emission controls over cities within these ranges. The range for primary PM2.5 (92km) is very different from that for secondary PM2.5 (515km). Cooperative emission controls of SO2 and NOx on a much larger regional scale are required to reduce the secondary PM2.5 in the YRD.

Molecular mechanism for rapid autoxidation in \u03b1-pinene ozonolysis

Aerosol affects Earth’s climate and the health of its inhabitants. A major contributor to aerosol formation is the oxidation of volatile organic compounds. Monoterpenes are an important class of volatile organic compounds, and recent research demonstrate that they can be converted to low-volatility aerosol precursors on sub-second timescales following a single oxidant attack. The α-pinene + O3 system is particularly efficient in this regard. However, the actual mechanism behind this conversion is not understood. The key challenge is the steric strain created by the cyclobutyl ring in the oxidation products. This strain hinders subsequent unimolecular hydrogen-shift reactions essential for lowering volatility. Using quantum chemical calculations and targeted experiments, we show that the excess energy from the initial ozonolysis reaction can lead to novel oxidation intermediates without steric strain, allowing the rapid formation of products with up to 8 oxygen atoms. This is likely a key route for atmospheric organic aerosol formation.

Effects of biomass burning and photochemical oxidation on the black carbon mixing state and light absorption in summer season

To investigate the effects of biomass burning and photochemical oxidation on the black carbon (BC) mixing state and light absorption, a tandem centrifugal particle mass analyzer (CPMA) and single-particle soot photometer (SP2) system was used to measure ambient fine particulate BC during EXPLORE-YRD 2018 campaign (EXPeriment on the eLucidation of the atmospheric Oxidation capacity and aerosol foRmation, and their Effects in Yangtze River Delta). The mass ratio (MR) of the non-BC coating to BC core, a morphology-independent parameter to quantify the mixing state of BC-containing aerosols, is derived. Two types of periods were identified, namely non-significant biomass-burning period (NB), and enhanced biomass burning period (EB). The MR was higher during EB (2.3 ± 0.5), compared with during the NB (2.0 ± 0.5). MR showed bimodal diurnal variation with peaks in the early morning and early afternoon, mainly due to the biomass burning and photochemical processes, respectively. The light-absorbing enhancement ranged from 1.0 to 1.19 when MR was from 1.4 to 3.4. The relationship of rBC mixing state and its optical properties was parameterized, which can further be used in the regional model.