Aerosol Fraction Research Articles

Tracing the provenance of mineral dust over the northern and southern Indian Oceans during the GEOTRACES-India (GI-01, GI-02) expeditions

Aeolian transport of mineral dust is an important carrier of nutrients and trace metals to the surface ocean and, hence, affects the biogeochemical cycles of C and N therein. Studies focusing on the provenances of dust across the latitudinal gradients over the open ocean waters are essential for better constraining the biogeochemical effects of dust deposition. Here, we analyzed the radiogenic isotope composition of Sr (87Sr/86Sr) and Nd (εNd(0)) in the silicate fraction of mineral aerosols collected over the pelagic northern and southern Indian ocean waters during the GEOTRACES-India research expeditions (GI-01: March-April 2014 and GI-02: April-May 2014). Both tracers, 87Sr/86Sr and εNd(0), exhibited marked spatial variability for dust deposition to different basins, including the Bay of Bengal (BoB), Arabian Sea (AS), equatorial Indian Ocean (EIO), and the southern sector of the Indian Ocean (SIO). The dust deposited in the AS showed a narrow spread in both 87Sr/86Sr (0.71520–0.71642) and εNd(0) (−10.9 to −10.1), along with the air mass back trajectories, indicating transport from the Arabian Peninsula. Likewise, the dust collected over the BoB was mainly sourced from the Thar Desert (87Sr/86Sr > 0.72, −16 < εNd(0) 〈−13), whereas the EIO received mineral dust from the Thar Desert and sand dunes in northern Australia (87Sr/86Sr: 0.72, εNd(0): −11) and Indonesian Archipelago. In contrast, the SIO appeared to receive dust deposition from three different source regions, including dust from Antarctica, western Australia (87Sr/86Sr: 0.712, −20 < εNd(0) <−16, and South Africa/South America (87Sr/86Sr: 0.708–0.710; −24.5 < εNd(0) >−8.4). These results have important implications for modelling the dust transport to pelagic Indian and southern Indian Ocean waters.

Retrieval of Aerosol Optical Depth and FMF over East Asia from Directional Intensity and Polarization Measurements of PARASOL

The advantages of performing aerosol retrieval with multi-angle, multi-spectral photopolarimetric measurements over intensity-only measurements come from this technique’s sensitivity to aerosols’ microphysical properties, such as their particle size, shape, and complex refraction index. In this study, an extended LUT (Look Up Table) algorithm inherited from a previous work based on the assumption of surface reflectance spectral shape invariance is proposed and applied to PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Science coupled with Observations from a Lidar) measurements to retrieve aerosols’ optical properties including aerosol optical depth (AOD) and aerosol fine-mode fraction (FMF). Case studies conducted over East China for different aerosol scenes are investigated. A comparison between the retrieved AOD regional distribution and the corresponding MODIS (Moderate-resolution Imaging Spectroradiometer) C6 AOD products shows similar spatial distributions in the Jing-Jin-Ji (Beijing–Tianjin–Hebei, China’s mega city cluster) region. The PARASOL AOD retrievals were compared against the AOD measurements of seven AERONET (Aerosol Robotic Network) stations in China to evaluate the performance of the retrieval algorithm. In the fine-particle-dominated regions, lower RMSEs were found at Beijing and Hefei urban stations (0.16 and 0.18, respectively) compared to those at other fine-particle-dominated AERONET stations, which can be attributed to the assumption of surface reflectance spectral shape invariance that has significant advantages in separating the contribution of surface and aerosol scattering in urban areas. For the FMF validation, an RMSE of 0.23, a correlation of 0.57, and a bias of −0.01 were found. These results show that the algorithm performs reasonably in distinguishing the contribution of fine and coarse particles.

Regional transport of aerosol above boundary layer and its radiation effect trigger severe haze pollution in Beijing

Contribution of the regional transported aerosol above planetary boundary layer (PBL), together with its radiation effect (AR), in triggering severe haze pollution in Beijing were investigated in this work. Both observations and model simulations of a polluted episode during Dec.14–16, 2018 indicated that regional transported aerosol above PBL was downwards transported and resulted in a fast increase in fine particulate matter (diameter < 2.5 μm, PM2.5) at ground level. Quantitative evaluation by sensitive simulations indicated that regional transported aerosol contributed 60.49 μg m−3 (55.1%) in total PM2.5 at ground level, and this contribution became even larger in the beginning stage (e.g., 14:00 on Dec.14) (70.3%). The transported aerosol stabilizes the boundary layer via its AR effect, which further enhances PM2.5 accumulation at ground level. PM2.5 at ground level further increased by 5.07 μg m−3 due to the AR effect of transported aerosol, contributing 77.8% in PM2.5 enhancement due to AR effect. Further analyses indicated that the high altitude of transported aerosol and higher fraction of black carbon in beginning stage were two factors that resulted in transported aerosol exerting more important role in PM2.5 enhancement than local aerosol. Hence, regional transported aerosol and its AR effect trigger rapid increase of PM2.5, exaggerate pollution level in Beijing.

Multiple Sulfur Isotopic Evidence for Sulfate Formation in Haze Pollution.

The mechanism of sulfate formation during winter haze events in North China remains largely elusive. In this study, the multiple sulfur isotopic composition of sulfate in different grain-size aerosol fractions collected seasonally from sampling sites in rural, suburban, urban, industrial, and coastal areas of North China are used to constrain the mechanism of SO2 oxidation at different levels of air pollution. The Δ33S values of sulfate in aerosols show an obvious seasonal variation, except for those samples collected in the rural area. The positive Δ33S signatures (0‰ < Δ33S < 0.439‰) observed on clean days are mainly influenced by tropospheric SO2 oxidation and stratospheric SO2 photolysis. The negative Δ33S signatures (-0.236‰ < Δ33S < ∼0‰) observed during winter haze events (PM2.5 > 200 μg/m3) are mainly attributed to SO2 oxidation by H2O2 and transition metal ion catalysis (TMI) in the troposphere. These results reveal that both the H2O2 and TMI pathways play critical roles in sulfate formation during haze events in North China. Additionally, these new data provide evidence that the tropospheric oxidation of SO2 can produce significant negative Δ33S values in sulfate aerosols.

Light-absorbing properties of polar- and non-polar brown carbon fractions of aerosols in Delhi

In the present study, PM2.5 samples (n = 104) were collected during February 2020–March 2021 on diurnal basis in Delhi (a site of Indo-Gangetic Plain (IGP)), with a view to investigate seasonal and diurnal patterns of ambient brown carbon (BrC) with consideration of their potential sources. Given that the polarity of ambient aerosol influences their chemical and physical processing in the atmosphere, we compared the light absorption properties of brown carbon (BrC) in PM2.5 samples extracted with three different solvents i.e., water, methanol, and n-hexane. Methanol extracts showed much stronger light-absorbing ability followed by water and hexane extracts in the wavelength range of 300–600 nm. Peak values of mass absorption coefficient (babs-BrC-365nm) were observed during post-monsoon season in both polar- (water-and methanol-soluble) and non-polar (n-hexane soluble) fractions of BrC, mainly due to the influence of biomass-burning (BB) aerosols. This point is further supported by air mass back trajectories which are well correlated with fire-count data, and marker species such as EC, OC and non-sea-salt K+. Comparison of babs-BrC-365nm, mass absorption efficiency (MAE365nm), absorption Ångstorm exponent (AÅE) and simple forcing efficiency (SFE300–700) from this study with that in published datasets reveal the significant contribution of biomass-burning activities to BrC absorption and abundance in the ambient atmosphere. Furthermore, the optical properties of HULIS (humic-like substances) (n = 40, during day- and nighttime) in post-monsoon (October – November 2020) and winter aerosols (January – February 2021) were also characterised. Based on UV–Vis analysis, similar average babs-365nm of HULIS was observed for daytime and nighttime samples i.e., 9.96 ± 3.8 and 9.89 ± 3.3 Mm−1, respectively in post-monsoon samples. Opposingly in winter period, significantly high daytime value of babs-365nm of HULIS (7.24 ± 2.7 M m−1) compared to that of nighttime (4.45 ± 2.8 M m−1) was found. These results along with indicative E2/E3 (ratio of absorbance at 250 nm and 365 nm, respectively) and AÅE values in HULIS fraction suggest a more significant contribution from regional crop-residue burning emission in the formation of HULIS in post-monsoon. While in winter period local emissions and subsequent secondary formation of HULIS are important. To the best of our knowledge, this study is the first attempt to investigate light absorption properties of different polarity BrC extracts (methanol, water, n-hexane, HULIS) in aerosol samples collected throughout the year at a representative site in Indo-Gangetic Plain (IGP).

The Vertical Distribution of Ice-Nucleating Particles over the North China Plain: A Case of Cold Front Passage

Ice-nucleating particles (INPs) are crucial for cloud freezing processes in the atmosphere. Given the limited knowledge about the vertical distribution of INPs and its relation to aerosols in China, we present two aircraft observations of INPs over the North China Plain on 23 October 2019 and 25 October 2019, before and after a cold front passage. We used a well-established method to identify the INPs on a silicon wafer and then performed single-particle chemical composition analysis using an environmental scanning electron microscope-energy dispersive spectrometer (ESEM-EDS). The INP concentrations range from 0.1 to 9.2 L−1 within activation temperatures from −20 to −29 °C. INPs are mostly concentrated within the boundary layer, and their concentration shows a decreasing trend with height (0.5~6 km) before the cold front passage. However, the highest INP concentration always appears at higher altitudes (4~5 km) after the cold front passage. The cold front passage also significantly weakens the correlations between the concentrations of INPs and aerosol particles at different sizes. The activated fraction (AF) of total aerosols increases from 10−6 to 10−4 with height from near ground to 6 km, reflecting a better nucleating capacity of the aerosols at higher altitudes. There is no obvious variation in AF after the cold front passage. Chemical analysis reveals that the INPs containing mineral dust components comprise the majority of total INPs during both flights. The proportion of pure mineral dust declines from 52.2% to 43.5% after the cold front passage while the proportion of mixed mineral dust increases from 23.9% to 45.7%, suggesting that an increased probability of aging or coating of INPs is introduced by the cold front during their long-distance transport. In addition, 88% of INPs have a diameter larger than 1 μm. This indicates that larger aerosols (&gt;1 μm) are the major contributors to INPs at high altitudes despite their relatively low abundance. Our results demonstrate a significant impact of transport events on the sources and vertical distribution of INPs in the atmosphere.

Influenza A and B Viruses in Fine Aerosols of Exhaled Breath Samples from Patients in Tropical Singapore.

Influenza is a highly contagious respiratory illness that commonly causes outbreaks among human communities. Details about the exact nature of the droplets produced by human respiratory activities such as breathing, and their potential to carry and transmit influenza A and B viruses is still not fully understood. The objective of our study was to characterize and quantify influenza viral shedding in exhaled aerosols from natural patient breath, and to determine their viral infectivity among participants in a university cohort in tropical Singapore. Using the Gesundheit-II exhaled breath sampling apparatus, samples of exhaled breath of two aerosol size fractions ("coarse" > 5 µm and "fine" ≤ 5 µm) were collected and analyzed from 31 study participants, i.e., 24 with influenza A (including H1N1 and H3N2 subtypes) and 7 with influenza B (including Victoria and Yamagata lineages). Influenza viral copy number was quantified using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Infectivity of influenza virus in the fine particle fraction was determined by culturing in Madin-Darby canine kidney cells. Exhaled influenza virus RNA generation rates ranged from 9 to 1.67 × 105 and 10 to 1.24 × 104 influenza virus RNA copies per minute for the fine and coarse aerosol fractions, respectively. Compared to the coarse aerosol fractions, influenza A and B viruses were detected more frequently in the fine aerosol fractions that harbored 12-fold higher viral loads. Culturable virus was recovered from the fine aerosol fractions from 9 of the 31 subjects (29%). These findings constitute additional evidence to reiterate the important role of fine aerosols in influenza transmission and provide a baseline range of influenza virus RNA generation rates.

Toxicity mechanisms of biomass burning aerosols in in vitro hepatic steatosis models

Nonalcoholic fatty liver disease (NAFLD) is a common chronic liver disease that contributes to the global rise in liver-related morbidity and mortality. Wood tar (WT) aerosols are a significant fraction of carbonaceous aerosol originating from biomass smoldering, contributing to air pollution particles smaller than 2.5 mm (PM2.5). Mechanistic biological associations exist between exposure to PM2.5 and increased NAFLD phenotypes in both cell and animal models. Therefore, this study examines whether an existing NAFLD-like condition can enhance the biological susceptibility of liver cells exposed to air pollution in the form of WT material. Liver cells were incubated with lauric or oleic acid (LA, OA, respectively) for 24 h to accumulate lipids and served as an in vitro hepatic steatosis model. When exposed to 0.02 or 0.2 g/L water-soluble WT aerosols, both steatosis model cells showed increased cell death compared to the control cells (blank-treated cells with or without pre-incubation with LA or OA) or compared to WT-treated cells without pre-incubation with LA or OA. Furthermore, alterations in oxidative status included variations in reactive oxygen species (ROS) levels, elevated levels of lipid peroxidation adducts, and decreased expression of antioxidant genes associated with the NRF2 transcription factor. In addition, steatosis model cells exposed to WT had a higher degree of DNA damage than the control cells (blank-treated cells with or without pre-incubation with LA or OA). These results support a possible systemic effect through the direct inflammatory and oxidative stress response following exposure to water-soluble WT on liver cells, especially those predisposed to fatty liver. Furthermore, the liver steatosis model can be influenced by the type of fatty acid used; increased adverse effects of WT on metabolic dysregulation were observed in the LA model to a higher extent compared to the OA model.

Unexpected moderate contribution of intermediate volatility organic compounds from gasoline vehicle emission to secondary organic aerosol formation in summer of Beijing

Intermediate volatility organic compounds (IVOCs) have been proposed to be important contributors to secondary organic aerosol (SOA) formation. In this study, we characterized ambient IVOCs in Beijing and performed a comprehensive closure study of ambient SOA production using top-down (photochemical-age-based parameterization method to apportion OA) and bottom-up (estimation of SOA from detailed speciation of IVOCs and VOCs) approaches. The IVOCs in Beijing were more oxidized and had a high abundance (62.5 ± 45.2 μg m−3), significantly higher than in the US. Unlike the US, the IVOCs in Beijing shows a hybrid characteristic of gasoline and vehicle exhausts and are influenced by complicated sources. A ∼ 80% SOA mass closure could be reached between the top-down and bottom-up methods, in which IVOCs was the dominant contributor (75.5%). Furthermore, we established a parametric method (SOA/CO vs. photochemical age) to estimate the contribution of vehicular SOA to ambient OA. Unexpectedly, the contributions of gasoline vehicles to ambient OA are only 7.3% for POA and 13.0% for SOA. Our results imply that IVOCs from other sources, e.g., diesel vehicles and cooking emissions, may be important precursors to secondary organic aerosol in Beijing. In addition, this study highlights the importance of comprehensively performing the molecular identification of IVOCs from different emissions in China. Plain language summarySecondary organic aerosol (SOA), formed by multigenerational oxidation of gas-phase compounds, represents a significant fraction of organic aerosol. However, current models often underestimate the measured SOA mass. One of the ubiquitous reasons is the missing measurement of the intermediate volatility organic compounds (IVOCs). Here we quantified and qualified the IVOCs in Beijing and performed a comprehensive SOA study using bottom-up and top-down methods. Besides, we estimate the SOA formation by gasoline vehicles. Unexpectedly, the contributions of gasoline vehicles to ambient OA are only 7.3% for POA and 13.0% for SOA, highlighting the importance of studying IVOCs from other sources, e.g., diesel exhausts and cooking emissions.

Thermodynamical framework for effective mitigation of high aerosol loading in the Indo-Gangetic Plain during winter

The Indo-Gangetic Plain (IGP) experiences severe air pollution every winter, with ammonium chloride and ammonium nitrate as the major inorganic fractions of fine aerosols. Many past attempts to tackle air pollution in the IGP were inadequate, as they targeted a subset of the primary pollutants in an environment where the majority of the particulate matter burden is secondary in nature. Here, we provide new mechanistic insight into aerosol mitigation by integrating the ISORROPIA-II thermodynamical model with high-resolution simultaneous measurements of precursor gases and aerosols. A mathematical framework is explored to investigate the complex interaction between hydrochloric acid (HCl), nitrogen oxides (NOx), ammonia (NH3), and aerosol liquid water content (ALWC). Aerosol acidity (pH) and ALWC emerge as governing factors that modulate the gas-to-particle phase partitioning and mass loading of fine aerosols. Six "sensitivity regimes" were defined, where PM1 and PM2.5 fall in the "HCl and HNO3 sensitive regime", emphasizing that HCl and HNO3 reductions would be the most effective pathway for aerosol mitigation in the IGP, which is ammonia-rich during winter. This study provides evidence that precursor abatement for aerosol mitigation should not be based on their descending mass concentrations but instead on their sensitivity to high aerosol loading.

Anthropogenic amplification of biogenic secondary organic aerosol production

Abstract. Biogenic secondary organic aerosols (SOAs) contribute to a large fraction of fine aerosols globally, impacting air quality and climate. The formation of biogenic SOA depends on not only emissions of biogenic volatile organic compounds (BVOCs) but also anthropogenic pollutants including primary organic aerosol, sulfur dioxide (SO2), and nitrogen oxides (NOx). However, the anthropogenic impact on biogenic SOA production (AIBS) remains unclear. Here we use the decadal trend and variability in observed organic aerosol (OA) in the southeast US, combined with a global chemistry–climate model, to better constrain AIBS. We show that the reduction in SO2 emissions can only explain 40 % of the decreasing decadal trend of OA in this region, constrained by the low summertime month-to-month variability in surface OA. We hypothesize that the rest of the OA decreasing trend is largely due to a reduction in NOx emissions. By implementing a scheme for monoterpene SOA with enhanced sensitivity to NOx, our model can reproduce the decadal trend and variability in OA in this region. Extending to a centennial scale, our model shows that global SOA production increases by 36 % despite BVOC reductions from the preindustrial period to the present day, largely amplified by AIBS. Our work suggests a strong coupling between anthropogenic and biogenic emissions in biogenic SOA production that is missing from current climate models.

Study of atmosphere parameters of the IVV-2M reactor hall

The paper presents the results of a study of radioactive noble gases and from decay products in the atmosphere of the reactor hall of the research nuclear reactor IVV-2M. The distribution of short-lived 88Rb and 138Cs activity by sizes of aerosol particles was measured in the range of 0.5–1000 nm. It is shown that radioactive aerosols are characterized by three main modes with AMTD 2–3 nm, 7–15 nm and 400 nm. About 70% of aerosol activity is due to 88Rb. The equilibrium factor between 88Kr and 88Rb is 0.2 ± 0.1. The total concentration of aerosols particles was measured using an aerosol diffusion spectrometer. The value of unattached fraction of radioactive aerosols in the atmosphere of reactor hall IVV-2M was f = 0.15–0.25 at the average total aerosol particles concentration from 20,000 cm−3 to 53,000 cm−3.

Long-term trends of aerosol and cloud fraction over Eastern China based on ground-based observations

We looked into the long-term variability of aerosols and clouds over Eastern China (EC) using MICAPS ground-based data from 1995 to 2019 and MODIS aerosol optical depth (AOD) retrieval from 2003 to 2019. The ground-based observed visibility (VIS) was used to characterize aerosol concentrations. Our study indicate that VIS shows a significant shift over EC in recent decades, as evidenced by falling (P1: 1995–2006)-flat (P2: 2007–2013)-rising (P3: 2014–2019) periods. Correspondingly, a change was observed in cloud fraction (CF) from a strong increase to a slow fluctuation during the three periods over the Beijing-Tianjin-Hebei (BTH), but no significant variation over the Yangtze River Delta (YRD) region. In addition, the CF-VIS shows a negative correlation during both P1 and P3 periods while this relationship weakened during P3 (35% weaker in BTH and 44% weaker in YRD). However, it is important to note that this weakening may be influenced by a few factors, such as data processing methods, the location of aerosols relative to the cloud, relative humidity (RH), and large-scale circulation etc. Further studies, including numerical simulations and analysis, are required to determine how much change of cloudiness is attributed to aerosols.

Identifying patterns of aerosols formation during contact butt fusion welding

The object of research is the hygienic characteristics of harmful substances that pollute the air during contact butt welding with continuous and pulsating melting. The task to be solved is the lack of such information for devising appropriate measures to protect operators of contact welding of railroad rails. A description of the methods of researching the chemical composition of welding aerosols and gases, the dispersed composition of nano-sized fractions of aerosols and assessing their impact on the body of welders is given. It was established that contact butt welding by melting P65 rails is accompanied by the release of harmful substances into the air of the working zone in the form of aerosols at the nano range level, which are characterized by high biological activity. The research results showed that during continuous melting, the intensity of welding aerosol release is lower than during pulsating melting. It is shown that the toxicity of the aerosol during contact welding belongs to the moderately dangerous class. It was established that during contact butt welding by melting, an aerosol is formed, the composition of which contains nano-sized components of manganese and iron in concentrations that exceed the calculated approximately safe levels of human exposure. In the aerosol sample, particles ranging in size from 70.8 to 1071.8 nm were detected, and the average aerodynamic diameter of the aerosol particles was 295.2 nm. The studies have shown that melting butt welding is accompanied by the formation of such toxic gases as nitrogen dioxide and carbon monoxide in concentrations that exceed the maximum permissible. The results of a comprehensive hygienic assessment of aerosols during contact butt fusion welding provided comprehensive information about the level of harmful effects of these aerosols on the body of welders

Effects of long-distance transport on O3 and secondary inorganic aerosols formation in Qingdao, China

This work presents a three-year continuous observation of ozone (O3) and fine particle (PM2.5), as well as their precursors in Qingdao, China, from September 2018 to August 2021. The annual concentrations of O3 and PM2.5 were measured as 35.9–44.5 ppbv and 31.6–34.2 μg m−3, respectively. Analysis of the interannual variations of O3 and PM2.5 concentration indicated the effective control measures for PM2.5 and O3 pollution in Qingdao in recent years. Nevertheless, we still observed 85 O3 episodes and 80 PM2.5 episodes during the whole observation. And it was found that the fraction of secondary inorganic aerosols (SIA) in PM2.5 mass significantly increased during PM2.5 episodes. By employing the Lagrangian photochemical trajectory model (LPTM), we investigated the roles of local production and regional transport (i.e., short-distance transport and long-distance transport) that play in the O3 and SIA formation in these episodes. The contribution of local production, short-distance transport, and long-distance transport to O3 concentration was calculated as 36%, 25%, and 39%, respectively. Long-distance transport seemed to play a more significant role in the SIA formation, accounting for 56% of SIA concentration. Moreover, the calculation results of the relative incremental reactivity (RIR) showed that both O3 and SIA formation were mainly affected by NOx and VOCs emissions during the process of long-distance transport. The observed unexpectedly high contribution of long-distance transport to O3 and SIA formation suggests that more extensive regional joint prevention and control policies on NOx and VOCs emissions are warranted to mitigate secondary air pollution.

Sulfur isotopes quantify the impact of anthropogenic activities on industrial-era Arctic sulfate in a Greenland ice core

Anthropogenic sulfate aerosols are estimated to have offset 60% of greenhouse-gas-induced warming in the Arctic, a region warming four times faster than the rest of the world. However, sulfate radiative forcing estimates remain uncertain because the relative contributions from anthropogenic versus natural sources to total sulfate aerosols are unknown. Here we measure sulfur isotopes of sulfate in a Summit, Greenland ice core from 1850 to 2006 CE to quantify the contribution of anthropogenic sulfur emissions to ice core sulfate. We use a Keeling plot to determine the anthropogenic sulfur isotopic signature (δ34Santhro = +2.9 ± 0.3 ‰), and compare this result to a compilation of sulfur isotope measurements of oil and coal. Using δ34Santhro, we quantify anthropogenic sulfate concentration separated from natural sulfate. Anthropogenic sulfate concentration increases to 67 ± 7% of non-sea-salt sulfate (65.1 ± 20.2 µg kg−1) during peak anthropogenic emissions from 1960 to 1990 and decreases to 45 ± 11% of non-sea-salt sulfate (25.4 ± 12.8 µg kg−1) from 1996 to 2006. These observations provide the first long-term record of anthropogenic sulfate distinguished from natural sources (e.g. volcanoes, dimethyl sulfide), and can be used to evaluate model characterization of anthropogenic sulfate aerosol fraction and radiative forcing over the industrial era.

Black carbon content of traffic emissions significantly impacts black carbon mass size distributions and mixing states

Abstract. Both the size and mixing state of black carbon (BC)-containing aerosols are crucial in estimating the environmental, health and climate impacts of BC. Traffic emissions are a major global source of BC; however, parameterization of BC mass size distributions and mixing states associated with traffic remains lacking due to its dependence on vehicle types and driving conditions. To investigate BC mass size distributions and mixing states associated with traffic emissions, a field campaign was conducted in the Guangzhou urban area during winter, which used a system coupling a differential mobility analyzer (DMA) and a single-particle soot photometer (SP2) to measure BC mass size distributions in the range of 100 to 700 nm. The resolved primary organic aerosols were hydrocarbon-like organic aerosols (HOA) and cooking-like organic aerosols (COA), as well as refractory BC (rBC), which was detected by the DMA–SP2 and correlated highly with HOA (R2=0.88), confirming that traffic emissions are the dominant source of atmospheric BC during the observations. The BC mass size distribution was found to be best fitted by a lognormal distribution, with a geometric mean (Dg,BC) of 258±16 nm, varying between 200 and 300 nm. During daytime, active formation of secondary nitrate and organic aerosols was observed, but it had little effect on the variations of BC mass size distributions. Further analyses revealed that Dg,BC was moderately correlated with rBC / HOA (R2=0.41) in a linear form of Dg,BC=34×rBC/HOA+177, demonstrating that the BC content of traffic emissions significantly impacts the BC mass size distributions. In addition, the size-dependent fractions of BC-containing aerosols in all types of aerosols (fBCc) and the fraction of identified externally mixed (bare/thinly coated) BC particles in all BC-containing aerosols (fext) were also characterized. It was found that the daytime secondary aerosol formation reduced both fBCc and fext, with the decrease in fext being more pronounced for larger particles, possibly due to the higher relative coating thickness. Variations in fext during nighttime were mainly controlled by the emission conditions. For example, fext for 600 nm particles decreased from 0.82 to 0.46 as rBC / HOA increased from 1 to 3.5, while the mass ratios of secondary aerosols to rBC varied little, demonstrating that the BC content also significantly affects the mixing states of freshly emitted BC from traffic emissions. This study suggests that BC content can be used as the key factor to parameterize both the BC mass size distribution and mixing states from traffic emissions, which warrants future comprehensive investigation. In addition, other sources such as biomass burning and coal combustion also contribute substantially to BC emissions, and it was important to investigate whether BC content of other major BC sources than traffic is also important in determining BC mass size distributions and mixing states. Overall, results of this study have significant implications for accurate representation of BC from different sources when modeling the impacts of BC.

A multiple-charging correction algorithm for a broad-supersaturation scanning cloud condensation nuclei (BS2-CCN) system

Abstract. High time resolution (∼1 s) of aerosol hygroscopicity and CCN activity can be obtained with a broad-supersaturation scanning cloud condensation nuclei (BS2-CCN) system. Based on a commercial CCNC (CCN counter), the newly designed diffusive inlet in the BS2-CCN realizes a broad-supersaturation distribution in a chamber with a stable, low sheath-to-aerosol-flow ratio (SAR). In this way, a monotonic relation between the activation fraction of aerosols (Fact) and critical activation supersaturation (Saerosol) can be obtained. The accuracy of the size-resolved aerosol hygroscopicity, κ, measured by the BS2-CCN system can be, however, hampered by multiply charged particles, i.e., resulting in the overestimation of κ values. As the BS2-CCN system uses multiple and continuous supersaturations in the chamber and the size-resolved Fact value is directly used to derive κ values, the multiple-charging correction algorithm of the traditional CCNC where single supersaturation is applied does not work for the BS2-CCN observation. Here, we propose a new multiple-charging correction algorithm to retrieve the true Fact value. Starting from the largest size bin, a new Fact value at a specific particle diameter (Dp) is updated from a measured activation spectrum after removing both aerosol and the CCN number concentration of multiply charged particles using a kernel function with a given particle number size distribution. We compare the corrected activation spectrum with laboratory aerosols for a calibration experiment and ambient aerosols during the 2021 Yellow-Sea Air Quality Studies (YES-AQ) campaign. It is noted that this algorithm is only applied to the monomodal particle distribution. The difference between corrected and measured κ values can be as large as 0.08 within the measured κ values that range between 0.11 and 0.37 among the selected samples, highlighting that the multiple-charge effect should be considered for the ambient aerosol measurement. Furthermore, we examine how particle number size distribution is linked to the deviation of activation spectra and κ values.

Highly Time-Resolved Apportionment of Carbonaceous Aerosols from Wildfire Using the TC-BC Method: Camp Fire 2018 Case Study.

The Camp Fire was one of California's deadliest and most destructive wildfires, and its widespread smoke threatened human health over a large area in Northern California in November 2018. To analyze the Camp Fire influence on air quality on a 200 km distant site in Berkeley, highly time-resolved total carbon (TC), black carbon (BC), and organic carbon (OC) were measured using the Carbonaceous Aerosol Speciation System (CASS, Aerosol Magee Scientific), comprising two instruments, a Total Carbon Analyzer TCA08 in tandem with an Aethalometer AE33. During the period when the air quality was affected by wildfire smoke, the BC concentrations increased four times above the typical air pollution level presented in Berkeley before and after the event, and the OC increased approximately ten times. High-time-resolution measurements allow us to study the aging of OC and investigate how the characteristics of carbonaceous aerosols evolve over the course of the fire event. A higher fraction of secondary carbonaceous aerosols was observed in the later phase of the fire. At the same time, the amount of light-absorbing organic aerosol (brown carbon) declined with time.

Emission of volatile organic compounds from landfill working surfaces: Formation potential of ozone and secondary organic aerosols

The working surface of landfills is an important source of volatile organic compounds (VOCs), which have received increasing attention because of their role in potentially forming ozone and secondary organic aerosols (SOAs). In this study, 99 monitoring datasets on VOC emissions from a landfill working surface were obtained in 9 months and used to evaluate their ozone formation potential (OFP) and SOA formation potential (SOAFP) from a statistical perspective and compared using various methods. December was found to have the highest total OFP and SOAFP caused by VOC emissions from the landfill working surface. Both the propylene equivalent concentration (PEC) and maximum incremental reactivity (MIR) methods indicated that oxygenated compounds, especially ethanol, contributed the most to the OFP, accounting for 16.1 %–95.4 % and 44.9 %–98.6 % of the total OFP during the entire observation period, respectively. The fraction aerosol coefficient (FAC) method highlighted the effect of aromatic hydrocarbons which contributed to over 97 % of the total SOAFP. In contrast, the SOA potential (SOAP) method indicated that both aromatic hydrocarbons and oxygenated compounds play important roles, contributing 26.6 %–93.9 % and 21.6 %–73.4 % of the total SOAFP, respectively. Based on their mechanisms and comprehensiveness, PEC and SOAP methods are considered more appropriate for evaluating the OFP and SOAFP of VOCs released from landfill working surfaces. The annual total OFP and SOAFP of VOCs from landfill working surfaces of China in 2020 were thus estimated as 1.5 × 104 t and 135 t, respectively, with high variations among different regions along with the population, waste management system, and the amount of landfilled waste. This study provides a comprehensive understanding of the potential impacts and evaluation methods of local waste landfills in the atmospheric environment from a statistical perspective.