Search

During the 2017 summertime Arctic cruise observation campaigns, we measured over 290,000 individual submicron particles and clustered them into two inorganic classes (dominated by sea salt, accounting for 38.6% by number fraction) and five organic classes (dominated by natural and anthropogenic organics, 61.4%), presenting a distinct difference in geographic distribution. In the high Arctic and marginal ice zone (81.1–84.6°N) compared with the low Arctic (Chukchi Sea, Svalbard, and Iceland, <80°N), ocean‐derived organic aerosols were more prevalent (73.6% vs. 37.1%). Specifically, we found sharp contrasts in the geographic distributions of OC‐Ca (organics internally mixed with calcium, 29.0% vs. 9.4%) and OC‐S (organics internally mixed with sulfate, 3.2% vs. 21.4%). Utilizing an explainable machine learning technique, we inferred that OC‐Ca was driven by wind‐blown sea ice and/or sea ice floes and/or bubble bursting within sea ice leads under low wind speed conditions in the high Arctic, while OC‐S tended to associate with elemental carbon, sulfate, and higher temperatures, potentially originating from combustion emissions at low latitude regions. Plain Language Summary: Knowledge of the mixing state of individual particles is essential for elucidating their sources, formation mechanisms, atmospheric processes, and assessing their climate effect in the Arctic atmosphere. Here, we investigated the origins and geographic distribution of organic aerosol types using a single‐particle aerosol mass spectrometer during the 8th Chinese Arctic Expedition Research Cruise (Chinese Research Vessel Xuelong) in the summertime over the Arctic Ocean. According to the mixing state, individual organic particles were classified into several ocean‐derived and anthropogenic types. Ocean‐derived types were prevalent in the high Arctic compared with that of anthropogenic type in the low Arctic, and their driven factors were different. Specifically, sea ice fraction was the most important driver for the generation of ocean‐derived OC‐Ca (an aerosol type of organics internally mixed with calcium). OC‐S (an aerosol type of organics internally mixed with sulfate) substantially increased in the low Arctic, most probably driven by combustion sources. Key Points: Submicron organic aerosol types show distinct geographic distributions in the summertime ArcticHigher number fraction of ocean‐derived submicron organic aerosols is observed in the high Arctic than the low ArcticThe proportion of sea ice coverage is a determining factor contributing to the spatial variability of OC‐Ca number fractions. [ABSTRACT FROM AUTHOR]

Nitrogen-containing organic compounds (NOCs) may potentially contribute to aqueous secondary organic aerosols, yet the different formation of NOCs in aerosol particles and cloud droplets remains unclear. With the in-situ measurements performed at a mountain site (1690 m a.s.l.) in southern China, we investigated the formation of NOCs in the cloud droplets and the cloud-free particles, based on their mixing state information of NOCs-containing particles by single particle mass spectrometry. The relative abundance of NOCs in the cloud-free particles was significantly higher than those in cloud residual (cloud RES) particles. NOCs were highly correlated with carbonyl compounds (including glyoxalate and methylglyoxal) in the cloud-free particles, however, limited correlation was observed for cloud RES particles. Analysis of their mixing state and temporal variations highlights that NOCs was mainly formed from the carbonyl compounds and ammonium in the cloud-free particles, rather than in the cloud RES particles. The results support that the formation of NOCs from carbonyl compounds is facilitated in concentrated solutions in wet aerosols, rather than cloud droplets. In addition, we have identified the transport of biomass burning particles that facilitate the formation of NOCs, and that the observed NOCs is most likely contributed to the light absorption. These findings have implications for the evaluation of NOCs formation and their contribution to light absorption. [ABSTRACT FROM AUTHOR]

Fog/Cloud processing of atmospheric particles changes their physiochemical properties, with profound impacts on atmospheric compositions, climate, and human health. These processes involve intricate physical and chemical processes of individual particles, which are often inadequately represented in current models that assume uniformly mixed aerosol compositions. The activation of particles as cloud condensation nuclei (CCN) or ice nuclei (IN), as well as their subsequent modification during fog/cloud processing, are greatly influenced by the unique physiochemical properties of individual particles. Since the 1990s, numerous observations have been conducted to investigate the physiochemical properties of individual droplet residual particles—those particles remaining after droplet evaporation. These particles serve as valuable tracers for understanding the fog/cloud processing of aerosols. In this review, we first compile the various sampling methods employed to collect individual fog/cloud residual particles and summarize the current understanding of the diverse particle types observed in various regions, including urban/industrial, marine/coastal, dusty, and remote areas. Specifically, we explore the size and chemically segregated activation of these particles, as well as the potential role of complex compositions in the aqueous formation of secondary components. We highlight the impact of mixed secondary compositions on the activation of particle types, including soot-containing, organic matters, sea salt, and dust particles. These works also emphasize the importance of understanding the heterogeneous compositions across individual particles for accurately assessing the formation of secondary species during fog/cloud processing. Furthermore, this review underscores the modification of microphysical properties of individual particles and their potential implications for optical properties and CCN/IN activities. Finally, we outline the limitations of current research on individual fog/cloud residual particles and identify areas for future investigation. • The chemical compositions and mixing structures of individual fog/cloud droplet residuals in various types of regions are summarized. • The activation and modification of particles involved in fog/cloud processing are tightly associated with individual particle properties. • The modification of cloud-processed individual particles and potential implications for evaluating their impacts are highlighted. [ABSTRACT FROM AUTHOR]

Mixing state of black carbon (BC) with secondary species has been highlighted as a major uncertainty in assessing its radiative forcing. While recent laboratory simulation has demonstrated that BC could serve as a catalyst to enhance the formation of sulfate, its role in the formation and evolution of secondary aerosols in the real atmosphere remains poorly understood. In the present study, the mixing of BC with sulfate/nitrate in the atmosphere of Guangzhou (China) was directly investigated with a single particle aerosol mass spectrometer (SPAMS). The peak area ratios of sulfate to nitrate (SNRs) for the BC‐containing particles are constantly higher than those of the BC‐free particles (defined as particles with negligible BC signals). Furthermore, the seasonal SNR peak is observed in summer and autumn, and the diurnal peak is found in the afternoon, consistent with the trends of radiation‐related parameters (i.e., solar radiation and temperature), pointing to the BC‐induced photochemical production of sulfate. Such hypothesis is further supported by the multilinear regression and random forest analysis, showing that the variation of SNRs associated with the BC‐containing particles could be well explained (R2 = ∼0.7–0.8) by the radiation‐related parameters (>30% of the variance) and the relative BC content (∼20%) in individual particles, but with limited influence of precursors (SO2/NOx: <5%). Differently, the radiation‐related factors only explain <10% of the SNR variation for the BC‐free particles. These results provide ambient observational evidence pointing to a unique role of BC on the photochemical formation and evolution of sulfate, which merits further quantitative evaluations. Plain Language Summary: Despite ubiquitous in the atmosphere, the potential role of BC black carbon (BC) in the formation and evolution of secondary aerosols in the real atmosphere remains poorly understood. Here, we have investigated the detailed mixing state of BC with sulfate/nitrate in the atmosphere of Guangzhou in real‐time by a Single Particle Aerosol Mass Spectrometer. We show that the distinct seasonal and diurnal variation of the enhanced sulfate/nitrate ratios is most likely driven by the BC catalytic photochemistry. Our results provide first ambient observational evidence, extending the laboratory results to the ambient atmosphere that BC could act as a photoactive and absorbing substrate, leading to an enrichment of sulfate, in particular, during summer and autumn. Thus, the BC emission controls may also mitigate the formation and evolution of sulfate and it is essential to include BC involved photochemistry in the models to account for the evolution and climate impact of BC accurately. Key Points: Enhanced sulfate to nitrate ratios (SNRs) are observed for the black carbon (BC)‐containing particlesThe distinct diurnal variation of the enhanced SNRs is most likely attributed to BC catalytic photochemistrySNRs in individual BC‐containing particles could be well predicted by the radiation‐related parameters and the relative BC content [ABSTRACT FROM AUTHOR]

Nitrophenols have received extensive attention due to their strong light-absorbing ability in the near-ultraviolet-visible region, which could be influenced by the atmospheric processes of nitrophenols. However, our knowledge and understanding of the formation and evolution of nitrophenols are still in the nascent stages. In the present study, the mixing states of four mononitrophenol particles (i.e., nitrophenol, methynitrophenol, nitrocatechol, and methoxynitrophenol), and one nitropolycyclic aromatic hydrocarbon particles (i.e., nitronaphthol (NN)) were investigated using a single-particle aerosol mass spectrometer (SPAMS) in November 2019 in Qingdao, China. The results showed, for the first time, that mononitrophenols and NN exhibit different mixing states and diurnal variations. Four mononitrophenols were internally mixed well with each other, and with organic acids, nitrates, potassium, and naphthalene. The diurnal variation in the number fraction of mononitrophenols presented two peaks at 07:00 to 09:00 and 18:00 to 20:00, and a valley at noon. Atmospheric environmental conditions, including NO 2 , O 3 , relative humidity, and temperature, can significantly influence the diurnal variation of mononitrophenols. Multiple linear regression and random forest regression models revealed that the main factors controlling the diurnal variation of mononitrophenols were photochemical reactions during the day and aqueous-phase reactions during the night. Unlike mononitrophenols, about 62–83% of NN were internally mixed with [NH 4 ]+ and [H(NO 3) 2 ]-, but not with organic acids and potassium. The diurnal variation of NN was also different from that of mononitrophenols, generally increased from 17:00 to 10:00 and then rapidly decreaed from 11:00 to 16:00. These results imply that NN may have sources and atmospheric processes that are different from mononitrophenols. We speculate that this is mostly controlled by photochemical reactions and mixing with [NH 4 ]+, which may influence the diurnal variation of NN in the ambient particles; however, this requires further confirmation. These findings extend our current understanding of the atmospheric formation and evolution of nitrophenols. [Display omitted] • Five nitrophenols were analyzed by a single-particle aerosol mass spectrometer. • Mononitrophenols and nitronaphthol have different mixing state and diurnal variation. • Photochemistry and aqueous-phase reactions control the diurnal variation of mononitrophenols. • [NH 4 ]+ can significantly influence the diurnal variation of nitronaphthol. [ABSTRACT FROM AUTHOR]

Although recent laboratory simulations have demonstrated that organic matter prevents the degradation of polycyclic aromatic hydrocarbons (PAHs), their role in the long-range transport of PAHs in the real atmosphere remains poorly understood. In this study, we measured the chemical composition and mixing state of PAHs-containing individual particles in aerosols from three sources, one urban area and one remote area. PAHs-containing particles were classified into five types: organic carbon (OC), potassium mixed with organic carbon (KOC), potassium mixed with sodium (KNa), Krich and PAH-rich. The PAH-rich and KOC particles were the main types of particles produced by vehicle exhaust/coal burning and biomass burning, respectively, accounting for >50% of the PAHs-containing particles. It was found that organic matter enhancement of PAHs-containing particles occurs in the ambient atmosphere, with organic-rich (OC and KOC) particles accounting for >90%. Further analysis revealed that the increase in the fractions of PAHs was related to the mixing state with organic compounds due to the protection of organics against PAHs and/or the aging of PAHs-containing particles. The results of this study improve our understanding of the chemical composition and mixing state of PAHs particles in atmospheric aerosols from emission sources and urban and remote areas, and provide field observation evidence to support the promotion of the study of long-range transport of PAHs by organics. • The mixing state of PAHs particles from sources and ambient aerosols were obtained. • A significant fraction of KOC-PAHs particles was found in biomass burning aerosols. • Organics enhanced in PAHs-containing particles during atmospheric transport. • The mixing degree of organics and PAHs is closely related to its high abundance. [ABSTRACT FROM AUTHOR]

Continuous ambient measurement of atmospheric aerosols was performed with a single particle aerosol mass spectrometer (SPAMS) in Guangzhou during summer of 2012. The aerosols mainly consisted of carbonaceous particles as major compositions in submicrometer range, including K-rich (29.8%), internally mixed organics and elemental carbon (ECOC, 13.5%), organic carbon-rich (OC, 18.5%), elemental carbon (EC, 12.3%) and high molecular OC (HMOC, 3.2%), and inorganic types (e.g., Na-rich Na-K, Fe-rich, V-rich, and Cu-rich) as major ones in supermicrometer range. Results show that carbonaceous particles were commonly internally mixed with sulfate and nitrate through atmospheric processing, in particular, with sulfate; inorganic types were dominantly internally mixed with nitrate rather than sulfate, indicative of different evolution processes for carbonaceous and inorganic particles in the atmosphere. It was observed that variations of these particle types were significantly influenced by air mass back trajectories (BTs). Under the influence of continental BTs, carbonaceous types were prevalent, while Na-K and Na-rich types considerably increased when the BTs originated from south marine regions. Number fraction of carbonaceous types exhibited obvious diurnal variation throughout the sampling period, which reflects their relatively stable emission and atmospheric processes. Two EC particle types LC-EC and NaK-EC showed different diurnal distributions, suggesting their different origins. The obtained information on the mixing state and the temporal variation of particle types is essential for developing an understanding on the origin and evolution processes of atmospheric aerosols. [ABSTRACT FROM AUTHOR]

Abstract: The mixing state of elemental carbon (EC) with secondary species has been highlighted as a major uncertainty in assessing its climate impact. However, the extent to which secondary coatings are present on EC and the underlying processes remained poorly understood in China, where there is a high loading of EC produced from extensive usage of fossil fuels and biomass. A single particle aerosol mass spectrometer (SPAMS) was applied to detect the chemical compositions associated with EC at the Guangdong Atmospheric Supersite, China. Efforts were made to track the variation of secondary coatings on EC. It is the first report on the direct observation of secondary compositions associated with EC with high time resolution in China. The hourly average number of EC-containing particles accounted for ∼33% (21–50%) of total analyzed particles over the sampling period. EC was found to be extensively internally mixed with sulfate (97.4% in number), nitrate (89.5%), oxidized organics (69.6%), and/or ammonium (80%). The results also indicate that secondary processing on EC in condensation (0.2–0.5 μm) and droplet (0.7–1.1 μm) modes is different. Active photochemical formation of oxidized organics and ammonium sulfate during daytime, and formation of ammonium nitrate during nighttime led to a distinct diurnal circle of mixing state of EC in the condensation mode. However, the photochemical aging may have limited or negligible influence on the mixing state and growth of EC in the droplet mode. These findings improve the understanding of the evolution of physicochemical properties of EC, and may help to model its climate impact. [Copyright &y& Elsevier]

Highlights: [•] Number fraction of Fe-containing particles varied from <1% to 15%. [•] Fe-containing particles in Shanghai most correspond to anthropogenic sources. [•] Dust is suspected to be more responsible for the spike of Fe-containing particles. [•] Anthropogenic Fe aerosol tended to associate with secondary species. [Copyright &y& Elsevier]

Abstract: Trimethylamine (TMA) plays an important role in atmospheric chemistry, yet its pathway towards aerosol is not clear. We report in this study the measurement of TMA in submicron particles using a single particle aerosol mass spectrometer (SPAMS) in urban Guangzhou, China for the period of 30 April through 22 May, 2010. The number fraction of TMA-containing particles relative to total detected particle number dramatically increased within the occurrence of fogs. It changed from an average of ∼7% for clear days to ∼35% for the fog events. For particles with size larger than 0.5 μm, the fraction could even account up to ∼60%. Averaged relative intensity of TMA was correlated well with relative humidity, indicating the important role of aerosol water content in the gas-to-particle partitioning of TMA. During the fog events, number based size distribution of TMA-containing particles shifted towards larger mode, peaking at droplet mode (0.5–1.2 μm), corresponding to the build-up of aerosol mass, suggesting the significant mass transfer of TMA and other semi-volatile species from gas to aerosol. Results also reveal that most of TMA-containing particles also contained signals from ammonium, nitrate and sulfate. A much larger fraction of TMA-containing particles was found to contain nitrate during the fog events than on clear days. During the fog events, nitrate and sulfate were more strongly associated with TMA compared to ammonia, which was oppositely observed on clear days. These results indicate that gas-to-particle partitioning of TMA in urban Guangzhou occurs preferentially during fog processing. The study could help improve our understanding in fog processing and potential roles of TMA-containing particles in urban Guangzhou. [Copyright &y& Elsevier]

Abstract: Single particle aerosol mass spectrometer (SPAMS) was used to characterize the single particle size and chemical composition of submicron aerosols in the urban area of the Pearl River Delta region, China, for the period April 30 through May 22, 2010. A total of 696,465 particles were sized and chemically analyzed with both positive and negative ion spectra, in which 141,338 biomass burning particles were identified representing a significant source of submicron particles ∼20.3% by number. The results have revealed that biomass burning particles have experienced extensive atmospheric processing, finding that as much as 90.5% of the particles have internally mixed with secondary inorganic species. Biomass burning particles were clustered into six distinct particle groups, comprising of K–Ca-rich, K–Na-rich, K–organic carbon (K–OC), K–elemental carbon (K–EC), K–the mixture of OC and EC (K–OCEC) and K–Secondary. K–OC was the largest contributor with a fraction of 22.9%, followed by K–Secondary type (21.4%) and K–OCEC (19.0%). K–Na-rich type was observed in 11.9% of the particles and 90% internally mixed with EC. The fraction of nitrate in biomass burning particles was 10% higher than in the non-biomass burning particles. The sodium and potassium in biomass burning particles could exhibit high affinity for nitrate gases during neutralization reactions, facilitating the particulate nitrate formation. Meanwhile, the particulate sulfate in particles in the droplet-mode size was also enhanced. The results added appreciably to the knowledge of aerosol characteristics in the PRD region atmosphere and could be applied to the climate models. [Copyright &y& Elsevier]

The rapid development of cities and economic prosperity greatly motivates the growth of vehicular exhaust particles, especially the diesel-exhausted particles from the large fleet of passenger and freight, which present profound implications on climate, air quality, and biological health (e.g., pulmonary, autoimmune and cardiovascular diseases). As important physiochemical properties of atmospheric aerosols, however, the mixing state and effective density of individual particles emitted from diesel-powered vehicles under different driving conditions and their environmental implications remain uncertain. Here, a single-particle aerosol mass spectrometer (SPAMS) was used to investigate the chemical composition and vacuum aerodynamic diameter (D va), along with the aerodynamic diameter (D a) from an aerodynamic aerosol classifier (AAC), to determine the effective density of primary particles emitted from a light- duty diesel vehicle (LDDV) under the launching and idling engine states. Interestingly, the particle types and effective density appear to vary significantly with the engine status. A single particle type of Ca-rich particles, named Na-Ca-PAH, was predominant in the idling state, whose chemical components may be affected by the lubricants and incomplete combustion, contributing to a higher effective density (0.66 ± 0.21 g cm−3). In contrast, launching particles exhibited a lower effective density (0.34 ± 0.17 g cm−3) because of the substantial elemental carbon (EC). In addition, the effective density depends not only on the particle size but also on the chemical components with various abundances. EC and Ca play opposite roles in the effective density of LDDV emissions. Notably, a higher proportion of polycyclic aromatic hydrocarbons (PAHs) was observed in the idling particles, contributing to 78 ± 1.2%. Given the high contribution to these PAH-containing particles in the idling state, indispensable precautions should be taken at bus stops or waiting for pedestrians. This study provides more comprehensive insights into the initial characteristics of LDDV particles due to the launching and idling states, which is beneficial for improving the model results of source apportionment and understanding its environmental behavior regarding human health. [Display omitted] • The majority of diesel vehicle-exhausted particles at the launching state is EC. • More Ca-rich particles are emitted from diesel vehicle at the idling state. • A high proportion of PAH-containing particles was observed at the idling state. • Effective densities are different to various particle types of vehicular exhaust. [ABSTRACT FROM AUTHOR]

Amines are ubiquitous in the environment and pose potential impacts on atmospheric chemistry; however, their seasonal variations and atmospheric processes remain unclear. In this study, a single-particle aerosol mass spectrometer is employed to investigate the seasonal variations of amine-containing particles as well as the oxidation of trimethylamine (TMA) in the urban region of Guangzhou, China. Number fractions of the amine-containing particles exhibit distinct seasonal variations, with higher fractions in spring and summer. Four amines, namely, TMA, diethylamine (DEA), dipropylamine, and tripropylamine are observed over all the seasons. DEA and TMA are the most dominant and account for approximately 90% of all these amine-containing particles. They are mainly clustered into eight types, comprised of internally mixed organics and elemental carbon (OCEC), OC–K, EC, Metal–rich, Dust, NaK–EC, Amine–rich, and high molecular weight organic compounds. DEA and TMA distribute differently over particle types and exhibit a distinct mixing state because of their different physicochemical properties. Compared with TMA, DEA is associated with more sulfate. The possible oxidation of TMA is also investigated, and the results indicate the potential contribution of aqueous oxidation or NO 3 radical oxidation to the formation of TMA oxide. Overall, the results improve the comprehension of the formation and evolution processes of amines in atmospheric environment. • The number fraction of amine-containing particles in spring/summer is higher. • Trimethylamine and diethylamine distribute differently over particle types. • Compared with trimethylamine, diethylamine is associated with more sulfate. • A large fraction of trimethylamine is observed to be oxidized mainly at night. [ABSTRACT FROM AUTHOR]

While aerosol plays a significant role in the formation of cloud, the in-cloud scavenging of chemically segregated particle types were still insufficiently investigated and the controlling factors remain ambiguous. Several field observations were carried out during 2018–2021 at Mt. Tianjing (1690 m a.s.l.) in southern China, based on ground-based counterflow virtual impactor (GCVI)-single particle aerosol mass spectrometer (SPAMS), to investigate the in-cloud scavenging (activation) of various particle types, including black carbon (BC), organic-containing particles (OC), mineral dust (Dust), metal-containing particles (Metal), potassium-rich particles (K-rich) and sea salt (SS). GCVI was used to sample cloud droplet residual particles (Res) while PM 2.5 inlet sampled interstitial particles (Inter) during cloud events and ambient particles (Amb) on sunny days, respectively. Different types of particles were recognized based on spectral characteristics obtained by the SPAMS. Based on the coupled GCVI-SPAMS measurements, the number-based scavenging efficiencies (NSEs) of various particle types could be quantified. Besides, the influence of liquid water content (LWC), PM 2.5 , particle size, and mixing state on the NSEs were discussed. The NSE of SS was the highest (32.4%) while OC showed the lowest NSE (9.1%). Other particle types shared similar NSEs with all the detected particles, with an average of ∼20–25%. Apart from OC, NSEs of other types of particles increased with the increase of LWC and decreased with the increase of the concentration of PM 2.5 , suggesting that numerous PM 2.5 suppressed particles entering cloud droplets via competing for water vapor. The annual variations of NSEs were generally in accordance with LWC and PM 2.5 , reflecting the certain role of these environment conditions. The NSEs typically increased with particle size in a range of 0.2–2.0 μm, reflecting the dominant nucleation mechanism during in-cloud scavenging. Particles mixed with sulfate and nitrate were easier to be scavenged than those coated with organic compounds, e.g., the discrepancy reached 11.8% for the K-rich particles. [Display omitted] • In-cloud scavenging efficiencies for six chemically segregated aerosol types are firstly reported. • SS displayed the highest NSE (32.4% on average) while OC's NSE was the lowest (9.1%). • The annual variations of NSEs were generally in accordance with LWC and PM 2.5 level. • Sulfate and nitrate enhance the NSEs of BC and K-rich particles by ∼10% compare with organics. [ABSTRACT FROM AUTHOR]

Elemental carbon (EC) aerosol represents an important fraction of aerosol particles in urban area of the Pearl River Delta (PRD) region, China. Previous studies have demonstrated that EC particles in the PRD region undergo significant amounts of aging processes. To assess the degree of aging, the real-time single particle volatility of EC-containing particles was measured in an urban area of the PRD region by a thermodiluter coupled to a single particle aerosol mass spectrometer (SPAMS). The size and chemical composition of the individual particles before and after heating to 75 °C, 150 °C and 300 °C were characterized. Of the total unheated particles examined by SPAMS, 53% of the unheated particles contained EC, and a higher number fraction (69%) was observed in the particles heated to 300 °C. No significant differences in the mass spectral patterns were found between ambient temperature and 75 °C. Nitrate evaporated at 150 °C, and most of sulfate evaporated at 300 °C. EC-containing particles were clustered into four distinct particle types based on the dominant chemical species present in the mass spectra, comprised of EC, internally mixed EC and organic carbon (OC) (ECOC), internally mixed EC and sodium/potassium salt (NaK–EC), and internally mixed EC and metal species (Metal–EC). Detail analysis show that the volatility of EC-containing particles relied on the EC particle types. Among the four types, the EC type was quite volatile. A significant fraction of sulfate and organics in the ECOC type did not volatilize at 300 °C. The volatilities of secondary ions in the four EC-containing particle types were found to be dependent on their molecular composition. Additionally, the volatility of EC-containing particles decreased during the polluted hazy days due to the generation of low volatile compounds under the atmospheric conditions with higher precursor concentrations and oxidation capacity. To our knowledge, this is the first reported real-time volatility measurements of individual ambient aerosols in the PRD region. These findings provide an improved understanding of the aging process of EC particles, and may help in the modeling of its climate impact. [ABSTRACT FROM AUTHOR]

Inland transported sea spray aerosol (SSA) particles along with multiphase reactions are essential to drive the regional circulation of nitrogen, sulfur and halogen species in the atmosphere. Specially, the physicochemical properties of SSA will be significantly affected by the displacement reaction of chloride. However, the role of organic species and the mixing state on the chloride depletion of SSA during long-range inland transport remains unclear. Hence, a single particle aerosol mass spectrometer (SPAMS) was employed to investigate the particle size and chemical composition of individual SSA particles over inland southern China during the East Asian summer monsoon. Based on the variation of chemical composition, SSA particles were clustered into SSA-Aged, SSA-Bio and SSA-Ca. SSA-Aged was regarded as the aged Na-rich SSA particles. In comparison to the SSA-Aged, SSA-Bio involved some extra organic species associated with biological origin (i.e., organic nitrogen and phosphate). Each type occupies for approximately 50% of total detected SSA particles. Besides, SSA-Ca may relate to organic shell of Na-rich SSA particles, which is negligible (~3%). Tight correlation between Na and diverse organic acids was exhibited for the SSA-Aged (r2 = 0.52, p < 0.01) and SSA-Bio (r2 = 0.61, p < 0.01), reflecting the impact of organic acids to the chloride displacement during inland transport SSA particles. The chloride depletion occupied by organic acids is estimated to be up to 34%. It is noted that distinctly different degree of chloride depletion was observed between SSA-Aged and SSA-Bio. It is more likely to be attributed to the associated organic coatings for the SSA-Bio particles, which inhibits the displacement reactions between acids and chloride. As revealed from the mixing state of SSA-Bio, defined hourly mean peak area ratio of Cl / Na increases with the increasing phosphate and organic nitrogen. This finding provides additional basis for the improvement of modeling simulations in chlorine circulation and a comprehensive understanding of the effects of organics on chloride depletion of SSA particles. Unlabelled Image • Organic acids considerably contribute to chloride depletion of sea spray aerosol (SSA) particles. • The SSA particles are heavily internally mixed with biological compositions. • Biological organic coatings may inhibit heterogeneous reactions of SSA particles. [ABSTRACT FROM AUTHOR]

The effect of the mixing state of black carbon (BC) on light absorption is of enduring interest due to its close connection to regional/global climate. Herein, we present concurrent measurements of both BC absorption enhancement (E abs) and the chemical mixing state in southern China. E abs was obtained by simultaneous measuring the light absorption coefficient using an aethalometer before and after being heated. The observed E abs was categorized into non- (E abs ≤ 1.0), slight (1.0 < E abs ≤ 1.2), and higher (E abs > 1.2) enhancement groups, and it was compared to the mixing state of elemental carbon (EC) particles detected by a single particle aerosol mass spectrometer (SPAMS). The individual EC-containing particles were classified into four types, including EC with sodium and potassium ion peaks (NaK-EC), long EC cluster ions (C n +/−, n ≥ 6) with sulfate (EC-Sul1), short EC cluster ions (C n +/−, n < 6) with sulfate (EC-Sul2), and EC with OC and sulfate (ECOC-Sul). NaK-EC and EC-Sul2 are the dominant EC types. Slight enhancement group is mainly explained by the photochemical production of ammonium sulfate and organics on EC-Sul2 during afternoon hours. In contrast, the higher E abs is primarily attributed to the enhanced mixing of ammonium chloride with NaK-EC during morning hours, without photochemistry. The characterization of source emissions indicates that NaK-EC is likely from coal combustion and is associated with a relatively higher amount of ammonium chloride. To our knowledge, this is the first report to state that EC particles associated with ammonium chloride have a relatively higher E abs. Unlabelled Image • Both BC absorption enhancement (E abs) and mixing state were measured in real-time. • The morning E abs peak is explained by primary emission. • Secondary composition contributes to the afternoon E abs peak. • Internally mixed ammonium chloride is more responsible for the higher E abs. [ABSTRACT FROM AUTHOR]

Interactions between clouds and black carbon (BC) represent a significant uncertainty in aerosol radiative forcing. To investigate the influence of cloud processing on the scavenging of BC, concurrent measurement of individual cloud droplet residue particles (cloud RES) and interstitial particles (cloud INT) throughout a cloud event was deployed at Mt. Tianjing (1690 m a.s.l.) in southern China. An aethalometer (AE-33), a single particle aerosol mass spectrometer (SPAMS) and a scanning mobility particle sizer (SMPS) were used to investigate the mass concentration of equivalent BC (EBC), size-resolved number of BC-containing particles, and size-resolved number concentration of submicron particles in real-time, respectively. The number-based SEs of the submicron particles varied between 2.7 and 31.1%. Mass scavenging efficiency (MSE) ranged from 4.7% to 52.6% for EBC, consistent with the number-based SE (from 11.3% to 59.6%) of the BC-containing particles throughout the cloud event. Several factors that may influence the SEs of the BC-containing particles are considered and examined. SEs are most likely determined by a single factor, i.e., liquid water content (LWC), with R2 > 0.8 in a power function throughout the cloud event. Stage-resolved investigation of SEs further reveals that particle size matters more than other factors in the cloud formation stage, whereas there is an increasing role of the mixing state in the development and stability stage. We also observed lower SEs for the BC-containing particles internally mixed organics, consistent with previous literature. • The stage-resolved scavenging efficiency of BC particles is firstly reported. • Scavenging efficiency (SE) is dominantly controlled by liquid water content (LWC). • Key factors influencing the in-cloud SE of BC-containing particles are assessed. [ABSTRACT FROM AUTHOR]

• Pb-rich particles were mainly in the forms of PbO, PbCl 2 and Pb(NO 3) 2 in Beijing. • Pb-rich particles were mainly produced by coal combustion during heating period. • This is the first report of atmospheric processes producing toxic Pb(NO 3) 2 in China. • Increasing toxicity of Pb-rich particles may have negative environmental effects. A single particle aerosol mass spectrometry (SPAMS) was deployed to investigate the mixing state and chemical processing of Pb-rich particles in suburban Beijing. Based on a large dataset of mass spectra, Pb-rich particles were classified into Pb-O-Cl-N-S (55%), Pb-N (17%), Pb-N-S (15%), and Pb-EC (7%). Residual coal combustion, industrial activities, and meteorological conditions were identified as main factors regulating the variations of Pb-rich particles in the atmosphere. The highest abundance of the Pb-rich particles was observed during heating period (HP) primarily due to the increase in coal usage. Pb in Pb-O-Cl-N-S type was identified in forms of PbO, PbCl 2, and Pb(NO 3) 2. Dominantly presented in the form of Pb(NO 3) 2 , Pb-N type represented the completely transformed Pb-rich particles from PbO/PbCl 2 by atmospheric processes. It is found that PbCl 2 and PbO could be transformed to Pb(NO 3) 2 , highly dependent on the amount of NO 2 and RH. Significant enhancement of nitrate in Pb-O-Cl-N-S particles was observed when the RH was greater than 60%, emphasizing the importance of heterogeneous hydrolysis of N 2 O 5 on the formation of Pb(NO 3) 2. Compared with non-carcinogenic PbCl 2 /PbO and insoluble PbO, soluble and carcinogenic Pb(NO 3) 2 produced by atmospheric processes may significantly enhance negative effects of Pb-rich particles on human health and the ecosystem. [ABSTRACT FROM AUTHOR]