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Vehicle exhaust, as a major source of air pollutants in urban areas, contains a complex mixture of organic vapours including long-chain alkanes and aromatic hydrocarbons. The atmospheric oxidation of vehicle emissions is a highly complex system as inorganic gases (e.g. NOx and SO2) from other urban sources coexist and therefore remains poorly understood. In this work, the photooxidation of n-dodecane, 1,3,5-trimethylbenzene, and their mixture is studied in the presence of NOx and SO2 to mimic the atmospheric oxidation of urban vehicle emissions (including diesel and gasoline vehicles), and the formation of ozone and secondary aerosols is investigated. It is found that ozone formation is enhanced by higher OH concentration and higher temperature, but is influenced little by SO2 concentration. However, SO2 can largely enhance the particle formation in both number and mass concentrations, likely due to the promoted new particle formation and acid-catalysed heterogeneous reactions from the formation of sulfuric acid. In addition, organo-sulfates and organo-nitrates are detected in the formed particles, and the presence of SO2 can promote the formation of organo-sulfates. These results provide a scientific basis for systematically evaluating the effects of SO2, OH concentration, and temperature on the oxidation of mixed organic gases in the atmosphere that produce ozone and secondary particles.

Alkaline gases such as NH3 and amines play important roles in neutralizing acidic particles in the atmosphere. Here, two common gaseous amines (dimethylamine (DMA) and trimethylamine (TMA)), NH3, and their corresponding ions in PM2.5 were measured semicontinuously using an ambient ion monitor-ion chromatography (AIM-IC) system in marine air during a round-trip cruise of approximately 4000 km along the coastline of eastern China. The concentrations of particulate DMA, detected as DMAH+, varied from

Incense burning is a common religious activity that emits abundant gaseous and particulate pollutants into the atmosphere. During their atmospheric lifetime, these gases and particles are subjected to (photo-)oxidation, leading to the formation of secondary pollutants. We examined the oxidation of incense burning plumes under O3 exposure and dark condition using an oxidation flow reactor connected to a single particle aerosol mass spectrometer (SPAMS). Nitrate formation was observed in incense burning particles, mainly attributable to the ozonolysis of nitrogen-containing organic compounds. With UV on, nitrate formation was significantly enhanced, likely due to HNO3/HNO2/NOx uptake triggered by OH chemistry, which is more effective than ozone oxidation. The extent of nitrate formation is insensitive to O3 and OH exposure, which can be explained by the diffusion limitation on interfacial uptake. The OH-aged particles are more oxygenated and functionalized than O3-aged particles. Oxalate and malonate, two typical secondary organic aerosols (SOA), were found in OH-aged particles. Our work reveals that nitrate, accompanied by SOA, can rapidly form in incense-burning particles upon photochemical oxidation in the atmosphere, which could deepen our understanding of air pollution caused by religious activities.

Atmospheric particles can be viscous. The limitation in diffusion impedes the mass transfer of oxidants from the gas phase to the particle phase and hinders multiphase oxidation processes. On the other hand, nitrate photolysis has been found to be effective in producing oxidants such as OH radicals within the particles. Whether nitrate photolysis can effectively proceed in viscous particles and how it may affect the physicochemical properties of the particle have not been much explored. In this study, we investigated particulate nitrate photolysis in mixed sucrose-nitrate-sulfate particles as surrogates of atmospheric viscous particles containing organic and inorganic components as a function of relative humidity (RH) and the molar fraction of sucrose to the total solute (FSU) with an in situ micro-Raman system. Sucrose suppressed nitrate crystallization, and high photolysis rate constants (∼10-5 s-1) were found, irrespective of the RH. For FSU = 0.5 and 0.33 particles under irradiation at 30% RH, we observed morphological changes from droplets to the formation of inclusions and then likely "hollow" semisolid particles, which did not show Raman signal at central locations. Together with the phase states of inorganics indicated by the full width at half-maxima (FWHM), images with bulged surfaces, and size increase of the particles in optical microscopic imaging, we inferred that the hindered diffusion of gaseous products (i.e., NOx, NOy) from nitrate photolysis is a likely reason for the morphological changes. Atmospheric implications of these results are also presented.

In recent years, the frequent occurrence of haze and fog events in East and Central China has caused a serious reduction in atmospheric visibility and had a huge impact on human health. Based on the relative humidity, visibility and PM2.5 concentration, the occurrence frequencies of haze as well as the spatial and temporal variations of fog, haze and mist in China from 2013 to 2018 were analyzed. The occurrence frequency of the three weather phenomena increased from 2013 until 2016, and then decreased. Regarding seasonal distribution, haze days are concentrated in winter, while mist often appears in spring and autumn. Clean fog mainly occurs in high-mountain stations and clean areas with high relative humidity, while polluted fog is more common in densely populated cities. In Beijing, the proportion of clean weather increases year by year, PM2.5 in haze weather in Beijing mainly consists of organic carbon, nitrate, sulfate and other secondary aerosols. Most fog events are accompanied by air pollution. The dominant haze is humid haze, which means that its occurrence and aggravation are usually related to aerosol hygroscopic growth.

The relative humidity (RH) history that manifests the cycling of dehydration (water evaporation) and hydration (water uptake) may affect particle-phase reactions, products from which have strong influences on the physical properties and thus climatic effects of atmospheric particles. Using single-trapped particles, we show herein hygroscopic growths of mixed particles with reactive species undergoing three types of RH cycles, simulating different degrees of particle-phase reactions in the atmosphere. The reactive species are the widely known α-dicarbonyl glyoxal (GLY), and five reduced nitrogenous species, ammonium sulfate (AS), glycine (GC), l-alanine (AL), dimethylamine (DMA), and diethylamine (DEA). The results showed that the mixed particles after reactions generally had altered efflorescence relative humidity (ERH) and deliquescence relative humidity (DRH) values and reduced hygroscopic growths at moderately high RH (80%) conditions. For example, with an additional slow drying step, the mean mass growth factors at 90% RH during dehydration dropped from 2.56 to 2.02 for GC/GLY mixed particles and from 2.45 to 1.23 for AL/GLY mixed particles. The reduced hygroscopicity with more RH cycling will thus lead to less efficient light scattering of the mixed particles, thereby resulting in less cooling and exacerbating direct heating due to light absorption by the products formed.

Unexpectedly high amounts of aminium salts have been detected in ambient aerosol particles, prompting investigations into their role in new particle formation and nanoparticle growth. Amine uptake ...

Ozonolysis and autoxidation have been realized as important pathways for the heterogeneous ozone oxidation of polyunsaturated fatty acids, but the relative significance of these two pathways under ...

Atmospheric particles experience various physical and chemical processes and change their properties during their lifetime. Most studies on atmospheric particles, both in laboratory and field measurements, rely on analyzing an ensemble of particles. Because of different mixing state of individual particles, only average properties can be obtained from studies using ensembles of particles. To better understand the fate and environmental impacts of atmospheric particles, investigations on their properties and processes at a single-particle level are valuable. Among a wealth of analytic techniques, single-particle Raman spectroscopy provides an unambiguous characterization of individual particles under atmospheric pressure in a non-destructive and in-situ manner. This paper comprehensively reviews the application of such a technique in the studies of atmospheric particles, including particle hygroscopicity, phase transition and separation, and solute-water interactions, particle pH, and multiphase reactions. Investigations on enhanced Raman spectroscopy and bioaerosols on a single-particle basis are also reviewed. For each application, we describe the principle and representative examples of studies. Finally, we present our views on future directions on both technique development and further applications of single-particle Raman spectroscopy in studying atmospheric particles.

Aqueous-phase reactions between glyoxal (Gly) and methylaminium salts have been proposed to produce brown carbon (BrC). Yet, studies on their heterogeneous reactions and the effect of relative humi...

Short-chain alkyl amines can undergo gas-to-particle partitioning via reactive uptake by ammonium salts, whose phases have been thought to largely influence the extent of amine uptake. Previous studies mainly focused on particles of single ammonium salt at either dry or wet conditions without any addition of organic compounds. Here we report the uptake of dimethylamine (DMA) by ammonium sulfate (AS) and AS-sucrose mixed particles at different relative humidities (RHs) using an electrodynamic balance coupled with in situ Raman spectroscopy. DMA is selected as a representative of short-chain alkyl amines, and sucrose is used as a surrogate of viscous and hydrophilic organics. Effective DMA uptake was observed for most cases, except for the water-limiting scenario at5% RH and the formation of an ultraviscous sucrose coating at 10% RH and below. DMA uptake coefficients (γ) were estimated using the particle mass measurements during DMA uptake. Addition of sucrose can increase γ by absorbing water or inhibiting AS crystallization and decrease γ by elevating the particle viscosity and forming a coating layer. DMA uptake can be facilitated for crystalline AS or retarded for aqueous AS with hydrophilic viscous organics (e.g., secondary organic material formed via the oxidation of biogenic volatile organic compounds) present in aerosol particles.

Heinrich event 1 (H1) is an important millennial climate event during the last deglaciation. The substantial decreasing of monsoon strength in the East Asian monsoon region during the H1, as shown by stalagmite δ18O records, has been attributed to the southward shift of the intertropical convergence zone (ITCZ), which is caused by the slowdown/collapse of the Atlantic meridional overturning circulation (AMOC). However, records from different Asian monsoon regions show various trends in precipitation changes during the H1, and these trends cannot be solely interpreted by the southward shift of the ITCZ. In the present study, we reconstructed time-series of East Asian monsoon precipitation between 25,000 and 10,000 a BP from floodplain sediments in the Huai River Basin. A white sediment layer, distinct from other layers in the profile, contains significantly low TOC, tree pollen and fern spore contents, and more positive δ13Corg, and it is deposited during the H1 event. The determined TOC, pollen and δ13Corg time-series, together with previously reported stalagmite δ18O, indicate a catastrophic (severe) drought in Jianghuai Region, one of the East Asian monsoon regions, during the H1. The La Nina condition in tropical Pacific likely also contributes to the catastrophic drought in Jianghuai Region and the precipitation variations in the Asian monsoon region during the H1.

Reactive uptake by ammonium (NH4+) salts is one of the major pathways for the gas-to-particle partitioning of alkyl amines. Recent studies using particles of individual ammonium salts and mixtures with hydrophilic organics have revealed that the degree of amine uptake depends on the phase state of ammonium salts, the particulate water contents and particle viscosity. The role of hydrophobic organic compounds, another important category of particulate organics commonly detected in the ambient atmosphere, in amine uptake remains unknown. Here we report the uptake of dimethylamine (DMA) by ammonium sulfate (AS) particles coated with fresh or ozone-aged bulk oleic acid (OA) at 60%, 30%, and 4+ ions were displaced due to DMA uptake, except those conditioned at

Alkyl aminium sulfates (AASs) can affect the physicochemical properties of atmospheric aerosols such as hygroscopicity. Previous laboratory experiments have shown that the water content in AAS bulk solutions is higher than in aqueous ammonium sulfate solution in the range of 60–95% relative humidity (RH). Furthermore, amine was found to evaporate from the solution during the preparation of AASs from the parent amine and sulfuric acid solutions. Here we report the hygroscopicities of deposited particles of four AASs at different aminium-to-sulfate molar ratios (A/Ss) in the range of