Aerosol Sources Research Articles

A comparison of atmospheric aerosol absorption properties from the MERRA-2 reanalysis with AERONET

Our focus is the comparison of atmospheric aerosol absorption properties between the MERRA-2 reanalysis and the inversion product of the surface station network AERONET. We use the available Aerosol Absorption Optical Depth (AAOD) and Single Scattering Albedo (SSA) data from both sources during the period 1993–2022, for the globe. The comparison is performed for the whole dataset, but also repeated for different classifications, namely by aerosol types, Köppen climate, and continent. Moreover, we investigate the relationships between these classifications. For these medium and high optical depth cases, the MERRA-2 relative bias for AAOD and SSA is globally −3.7% and −1.4%, but there is a wide differentiation in performance for the different types, climates, and continents. The MERRA-2 SSA frequency distribution is too narrow compared to the AERONET. MERRA-2 strongly overestimates the absorption over N. America and less so over S. America and Europe, while it underestimates it greatly over Oceania. AAOD is underestimated over biomass-burning regions and overestimated over most areas rich in dust. There is evidence that the lack of brown carbon in the aerosol type classification scheme in MERRA-2 hampers its performance. The comparison over Asia dry areas (classified as Köppen climate type B) shows a large underestimation in AAOD, non-existent in other dry (B) climate types. For the relatively few observations over polar (Köppen type E) climates, MERRA-2 gives too absorptive aerosols. With respect to absorption properties, it appears that MERRA-2 would improve its agreement with AERONET by addressing some erroneous aerosol classifications, employing the brown carbon type, and introducing more detail in dry region aerosol sources.

Observations of atmospheric new particle formation impacts on cloud condensation nuclei in summer at Mt.Tian

As one of the important sources of aerosols, new particle formation events can affect the spatiotemporal distribution of CCN. To analyze the characteristics of new particle formation (NPF) events and their effects on cloud condensation nuclei (CCN) during the summer at Mt.Tian, the data of aerosol size distribution and CCN number concentrations were measured using an aerosol wide-range particle size spectrometer and a cloud condensation nuclei counter from August 4 to 25, 2019, and combined with meteorological data and polycyclic aromatic hydrocarbons (PAHs) data. NPF events at Mt.Tian occurred seven days during the observation period, accounting for 32% of the observation days, and usually occurred at 13:00 and ended at 17:00 (Beijing Time, same below). NPF events particularly influenced the diurnal variations of aerosol number concentrations in different modes. The number concentrations of nucleation and Aitken modes increased rapidly while the accumulation mode increased slowly during 13:00 and 17:00 on NPF days. The peak particle number concentrations in the nucleation, Aitken and accumulation modes on NPF days were 5360.1 cm−3, 7185.6 cm−3 and 839.3 cm−3, respectively, which were 3.3, 1.8 and 1.7 times higher than those on non-NPF days during 13:00 and 17:00. The meteorological conditions of temperature higher than 20 °C, air pressure lower than 806 hPa, relative humidity (RH) lower than 40% and wind speed higher than 2.2 m s−1 are favorable for the occurrence of NPF events. The NPF events at Mt.Tian can impact the mass concentration of PAHs. More Fluoride (FL) and Phenanthrene (PHE) were generated on NPF days. The mass concentrations of FL and PHE on NPF days were 0.002 ± 0.003 ng m−3 and 0.020 ± 0.010 ng m−3, which were 243.54% and 28.44% higher than those on non-NPF days, respectively. NPF events were conducive to increased CCN concentration at Mt.Tian. After the NPF events, the mean number concentrations of CCN at each supersaturation (SS) on NPF days was about 20%–50% higher than on non-NPF days. The contribution of NPF events to the CCN number concentrations was 35.75%, 28.56%, 44.15%, 42.11% and 29.12% at 0.1%, 0.2%, 0.4%, 0.6% and 0.8% SS, respectively.

Non-methane hydrocarbon characteristics and their ozone and secondary organic aerosol formation potentials and sources in the plate and logistics capital of China

Non-methane hydrocarbon (NMHC) is an important precursor of ozone (O3) and secondary organic aerosols (SOAs). As the plate and logistics capital of China, the characteristics and sources of NMHC in Linyi may differ from other areas. Therefore, to understand NMHC pollution characteristics and guide future control strategies, samples were collected from April to October 2021–2022 in Linyi to analysis NMHC concentration levels, ozone formation potential (OFP), secondary organic aerosol formation potential (SOAFP), and sources in different seasons. The NMHC concentrations in spring and summer were 100.1 ± 29.5 and 98.4 ± 31.7 μg/m3, respectively, higher than in autumn (83.7 ± 25.1 μg/m3) due to the re-outbreak of COVID-19 in Linyi in autumn. However, no difference was seen in the dominant NMHC contributors—oxygenated volatile organic compounds (OVOCs), alkane, and aromatics—among different seasons. Both the OFP and SOAFP of NMHC showed obvious seasonal variations with summer > spring > autumn. Promoting the use of non-formaldehyde adhesive and reducing 1, 3-diethylbenzene in organic synthesis are crucial for alleviating O3 and SOA pollution, respectively. Vehicle related, liquefied petroleum gas (LPG), natural gas (NG), solvent use, and the plate industry were the main NMHC sources in Linyi. The contribution of vehicle related and LPG/NG in autumn (13.7%) was lower than in spring (32.7%) and summer (29.4%), while the contribution of combustion in summer (5.7%) was lower than in spring (15.6%) and autumn (17.9%), consistent with the results of species-specific diagnostic ratios. Regional pollution transport was also analyzed. Although we encourage joint prevention and control regarding air pollution, the main areas of joint prevention and control should be different in different seasons, which can reduce adverse human effects and the consumption of material and financial resources.

Seasonal Variation and Source Identification of PM10 in an Industrialized City

AbstractA 1‐year PM10 sampling campaign from January 2019 to December 2019 is conducted in an urban industrial area Raipur, India. For the development of effective pollution control strategies, quantitative assessment of potentially toxic metals and accurate identification of pollutant sources are essential. The annual average PM10 aerosol mass concentration during the study period is recorded as 187.89 ± 91 µg m−3. PM10 concentrations are found to vary with meteorological parameters such as wind speed, temperature, rainfall, and humidity. Heavy metals including Fe, Mn, Ni, Pb, Zn, Al, Ba, Cr, Sr, Ga, Mg, and V are studied using atomic absorption spectroscopy (AAS). Seasonally, average winter time PM10 concentration (234.86 ± 104.3 µg m−3) is accounted higher as compared to summer (169.02 ± 27.1 µg m−3) and rainy season (106.28 ± 32.6 µg m−3) during the study period. The aerosol sources identified by positive matrix factorization (PMF) model are: iron and steel production (34.7%), vehicular emissions (29.3%), road dust (14.6%), heavy oil/petroleum (14.6%), and coal combustion (6.9%). Among these sources, iron and steel production contributes maximum in PM10 concentrations. The probable source locations are recognized through concentration weighted trajectory (CWT) analysis. The AirQ+ model is used to assess the health effects of regional PM10 concentrations.

Significant changes in size distribution of aerosols in Beijing after clean air actions

Over the past few years, the physicochemical characteristics and sources of aerosols have changed following the implementation of strict clean air policies in Beijing. In this study, size-segregated particulate matters (PM) were collected using a micro-orifice uniform deposit impactor (MOUDI) in Beijing from July 2021 to June 2022 to understand the responses of particle size distribution and chemical composition to the implemented emission reduction measures. The results showed that although particulate pollution greatly improved, it is still severe in Beijing, especially in autumn and winter, with the annual average PM1.8 (aerosol particle with aerodynamic diameter less than 1.8 μm) concentration reaching 46.7 ± 37.4 μg/m3. NO3− was the most abundant ion in the particles throughout all seasons, and its proportion to water-soluble inorganic ions increased significantly with the aggravation of pollution. This highlights the importance and urgency of controlling mobile sources in future control measures. The highest concentration of SO42− occurring during summer demonstrates the effectiveness of fossil fuel combustion control in winter. The measured size distributions of PM and secondary inorganic ions were trimodal, which significantly differed from the observations conducted in Beijing using MOUDI before 2017, in which the measured size distributions of PM and secondary inorganic ions were bimodal. The enhancement of atmospheric oxidation and reduction of gaseous precursors can affect the formation path of aerosols, and thus, their particle size distribution. Aerosol aqueous-phase reactions play a vital role in pollution development, with the droplet mode further growing hygroscopically into a coarse mode during pollution maintenance.

Cloud condensation nuclei activation properties of Mediterranean pollen types considering organic chemical composition and surface tension effects

Wind-dispersed pollen grains emitted from vegetation are directly injected into the atmosphere being an important source of natural aerosols globally. These coarse particles of pollen can rupture into smaller particles, known as subpollen particles (SPPs), that may act as cloud condensation nuclei (CCN) and affect the climate. In this study, we characterize and investigate the ability of SPPs of 10 Mediterranean-climate pollen types to activate as CCN. A continuous flow CCN counter (CCNC) was used to measure the activation of size-selected (80, 100 and 200 nm dry mobility diameter) particles at different supersaturations (SS). Hygroscopicity parameter (κ) for each SPP type and size has been calculated using κ-Köhler theory. Organic chemical speciation and protein content has been determined to further characterize pollen solutions. Furthermore, the surface activity of SPPs has also been investigated by using pendant drop tensiometry. All studied SPP samples show critical supersaturation (SSCrit) values that are atmospherically relevant SS conditions. Hygroscopicity κ values are in the range characteristic of organic compounds (0.1–0.3). We found that organic speciation and protein content vary substantially among pollen types, with saccharides and fatty acids being the only organic compounds found in all pollen types. A clear relationship between SPP activation and its organic composition was not observed. This study also reveals that all SPPs investigated reduce the surface tension of water at high concentrations but at diluted concentrations (such as those of activation in the CCNC), the water surface tension value is a good approximation in Köhler theory. Overall, this analysis points out that pollen particles might be an important source of CCN in the atmosphere and should be considered in aerosol-cloud interactions processes.

Analysis of Long‐Term Trends in the Vertical Distribution and Transport Paths of Atmospheric Aerosols in Typical Regions of China Using 15 Years of CALIOP Data

AbstractLong‐range transport and vertical distribution of aerosols are important factors for assessing the uncertainty in aerosol radiative forcing. This paper reveals the vertical distribution and trends of aerosol optical properties in China using 15 years of Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) data. The Hybrid Single‐Particle Lagrangian integrated trajectory model was used to analyze the transport and trends of aerosols in the layer with the highest occurrence frequencies of dust, polluted dust, polluted continental and elevated smoke aerosols. The results indicated that (a) there were significant regional and seasonal differences in the vertical distribution of aerosols. The aerosol optical depth (AOD) trend in a given region depends on the changes in the aerosol type with the highest frequency and the layer corresponding to the largest AOD in the vertical profile. The frequency of polluted dust aerosols was the highest in Beijing‐Tianjin‐Hebei (BTH) and Central China. The considerable decrease in the 0–2 km AOD led to a significant trend of the column AOD. (b) The changes of AOD and main aerosol types in a region are also affected by the changes of aerosol sources and long‐range transport pathways. In the BTH, dust aerosols originated from the Mongolian Plateau, accounting for 57.88% of the total trajectories. The Pearl River Delta was dominated by elevated smoke aerosols, with trajectories mainly originating from the Myanmar and Vietnam, accounting for 27.38% and 29.59%, respectively. The trend of 15‐year backward trajectories of dust aerosols on the Tibetan Plateau indicated that the trajectory from India is increasing.

Emission Factors of Carbonaceous Aerosol and Stable Carbon Isotope for In-use Vehicles

Vehicle exhaust is an important anthropogenic source of atmospheric carbonaceous aerosols; of which, the emission factors and stable carbon isotope composition are important basic data. In-use motor vehicles of different types were selected to conduct dynamometer tests using different test cycles and under cold/hot start conditions. The exhaust of each test stage was collected to analyze the carbonaceous components and stable carbon isotopes and to discuss the influencing factors. The total carbon emission factors follow the order:heavy-duty diesel vehicles>light-duty diesel vehicles>light-duty gasoline vehicles. Although the emission factors of light-duty natural gas vehicles were very low at the low- and medium-speed stages, they were similar to those of heavy-duty diesel vehicles at the high-speed stage. The emission factors of cold start were higher than those of hot start, and the emission factors of the NEDC test cycle were lower than those of WLTC (which should be related to the driving speed). The emission factors of organic carbon (OC) of gasoline and natural gas vehicles were much higher than those of elemental carbon (EC) in every test stage. The emission factors of OC and EC of diesel vehicles were similar. The OC/EC of all types of vehicles increased with the increase in driving speed. Stable carbon isotopes in EC were higher than those in OC. The stable carbon isotope in different vehicles follow the order:light-duty gasoline vehicles<light-duty natural gas vehicles<light-duty diesel vehicles<heavy-duty diesel vehicles. The results revealed that the source signatures of stable carbon isotope in vehicles used in current source apportionment could not well represent gasoline vehicles and natural gas vehicles. In future emission control and source apportionment, attention should be paid to the changes in emission factors and isotope signatures caused by the use of natural gas and the aging of motor vehicles.

Sources, sinks, and chemistry of Stabilized Criegee Intermediates in the Indo-Gangetic Plain

Night-time oxidation significantly affects the atmospheric concentration of primary and secondary air pollutants but is poorly constrained over South Asia. Here, using a comprehensively measured and unprecedented set of precursors and sinks of Stabilized Criegee Intermediates (SCI), in the summertime air of the Indo-Gangetic Plain (IGP), we investigate the chemistry, and abundance in detail. This study reports the first summertime levels from the IGP of ethene, propene, 1-butene, cis-2-butene, trans-2-butene, 1-pentene, cis-2-pentene, trans-2-pentene, and 1-hexene and their possible roles in SCI chemistry. Ethene, propene, and 1-butene were the highest ambient alkenes in both the summer and winter seasons. Applying chemical steady-state to the measured precursors, the average calculated SCI concentrations were 4.4 (±3.6) × 103 molecules cm−3, with Z-CH3CHOO (55 %) as the major SCI. Z-RCHOO (35 %) and α-pinene derived PINOO (34 %) were identified as the largest contributors to SCI with a 7.8 × 105 molecules cm−3 s−1 production rate. The peak SCI occurred during the evenings. For all SCI species, the loss was dominated (>50 %) by unimolecular decomposition or reactions with water vapor or water vapor dimer. Pollution events influenced by crop burning resulted in significantly elevated SCI production (2.1 times higher relative to non-polluted periods) reaching as high as (7.4 ± 2.5) × 105 molecules cm−3 s−1. Among individual SCI species, Z-CH3CHOO was highest in all the plume events measured accounting for at least ~41 %. Among alkenes, trans-2-butene was the highest contributor to P(SCI) in plume events ranging from 22 to 32 %. SCIs dominated the night-time oxidation of sulfur dioxide with rates as high as 1.4 (±1.1) × 104 molecules cm−3 s−1 at midnight, suggesting that this oxidation pathway could be a significant source of fine mode sulfate aerosols over the Indo-Gangetic Plain, especially during summertime biomass burning pollution episodes.

Harmful algal bloom aerosols and human health.

Harmful algal blooms (HABs) are increasing across many locations globally. Toxins from HABs can be incorporated into aerosols and transported inland, where subsequent exposure and inhalation can induce adverse health effects. However, the relationship between HAB aerosols and health outcomes remains unclear despite the potential for population-level exposures. In this review, we synthesized the current state of knowledge and identified evidence gaps in the relationship between HAB aerosols and human health. Aerosols from Karenia brevis, Ostreopsis sp., and cyanobacteria were linked with respiratory outcomes. However, most works did not directly measure aerosol or toxin concentrations and instead relied on proxy metrics of exposure, such as cell concentrations in nearby waterbodies. Furthermore, the number of studies with epidemiological designs was limited. Significant uncertainties remain regarding the health effects of other HAB species; threshold dose and the dose-response relationship; effects of concurrent exposures to mixtures of toxins and other aerosol sources, such as microplastics and metals; the impact of long-term exposures; and disparities in exposures and associated health effects across potentially vulnerable subpopulations. Additional studies employing multifaceted exposure assessment methods and leveraging large health databases could address such gaps and improve our understanding of the public health burden of HABs.

Trace metal dissolution kinetics of East Asian size-fractionated aerosols in seawater: The effect of a model siderophore

Aerosol soluble metals are considered bioavailable to marine phytoplankton and may influence phytoplankton growth, their community structure, and material cycling in the ocean. The dissolution is controlled by the physical and chemical properties of aerosols and various atmospheric, physical, and biogeochemical processes before and after depositing in the surface water. Among these complicated processes, the interaction of aerosol metals with organic ligands in seawater is one of the major factors. In this study, we systematically investigated the dissolution kinetics of trace metals from fine (0.45–0.95 μm) and coarse (>7.2 μm) aerosols in seawater for 30 days under conditions with or without adding a model Fe organic ligand, siderophore desferrioxamine B (DFB). We found that most of the soluble metals in the fine aerosols were leached rapidly within the first hour. In terms of the coarse aerosols, with DFB addition, the fractional solubility of Fe increased substantially from 0.1 to 10%, and the solubilities of most other metals generally increased by about 2-fold within 30 days. Without DFB addition, we found that most soluble metals were still gradually released over time in coarse aerosols, except particle-reactive metals, Fe and Pb. We further observed strong linear correlations between dissolved metals (Al, Fe, Mn, Co, Ni, and Zn) and silicate concentrations for DFB addition with coarse aerosols, with metal to silicate ratios comparable to those of typical aluminosilicates. Quantitatively, the aluminosilicate-associated dissolved metals accounted for >85% of total dissolved Fe, Al, and Co, and 40–60% for total dissolved Mn and Ni with the addition of DFB for 30 days. By comparing dissolved metal to Al ratios with lithogenic ratios, the metals leached in the first hour for both coarse and fine aerosols originated from anthropogenic sources, and lithogenic aerosols gradually became the dominant soluble metal source for coarse aerosols after 1 h, extending to 720 h. The findings of this study exhibit the importance of the time-dependent interaction of lithogenic aerosols with organic ligands in seawater. The residence time of aerosol particles and the concentrations of available organic ligands in the euphotic zone are key factors affecting aerosol dissolved metal availability to marine phytoplankton in the surface ocean.

Significant contributions of trimethylamine to sulfuric acid nucleation in polluted environments

As one of the least understood aerosol processes, nucleation can be a dominant source of atmospheric aerosols. Sulfuric acid (SA)-amine binary nucleation with dimethylamine (DMA) has been recognized as a governing mechanism in the polluted continental boundary layer. Here we demonstrate the importance of trimethylamine (TMA) for nucleation in the complex atmosphere and propose a molecular-level SA-DMA-TMA ternary nucleation mechanism as an improvement upon the conventional binary mechanism. Using the proposed mechanism, we could connect the gaseous amines to the SA-amine cluster signals measured in the atmosphere of urban Beijing. Results show that TMA can accelerate the SA-DMA-based new particle formation in Beijing by 50–100%. Considering the global abundance of TMA and DMA, our findings imply comparable importance of TMA and DMA to nucleation in the polluted continental boundary layer, with probably higher contributions from TMA in polluted rural environments and future urban environments with controlled DMA emissions.

Aerosol formation during foam application of non-volatile biocidal substances.

The application of biocidal products by foam is considered an alternative to droplet spraying when disinfecting surfaces or fighting infestations. Inhalation exposure to aerosols containing the biocidal substances cannot be ruled out during foaming. In contrast to droplet spraying, very little is known about aerosol source strength during foaming. In this study, the formation of inhalable aerosols was quantified according to the aerosol release fractions of the active substance. The aerosol release fraction is defined as the mass of active substance transferred into inhalable airborne particles during foaming, normalised to the total amount of active substance released through the foam nozzle. Aerosol release fractions were measured in control chamber experiments where common foaming technologies were operated according to their typical conditions of use. These investigations include foams generated mechanically by actively mixing air with a foaming liquid as well as systems that use a blowing agent for foam formation. The values of the aerosol release fraction ranged from 3.4 × 10-6 to 5.7 × 10-3 (average values). For foaming processes based on mixing air and the foaming liquid, the release fractions could be correlated to the process and foam parameters such as foam exit velocity, nozzle dimensions, and foam expansion ratio.

A 1-year aerosol chemical speciation monitor (ACSM) source analysis of organic aerosol particle contributions from anthropogenic sources after long-range transport at the TROPOS research station Melpitz

Abstract. Atmospheric aerosol particles are a complex combination of primary emitted sources (biogenic and anthropogenic) and secondary aerosol resulting from aging processes such as condensation, coagulation, and cloud processing. To better understand their sources, investigations have been focused on urban areas in the past, whereas rural-background stations are normally less impacted by surrounding anthropogenic sources. Therefore, they are predisposed for studying the impact of long-range transport of anthropogenic aerosols. Here, the chemical composition and organic aerosol (OA) sources of submicron aerosol particles measured by an aerosol chemical speciation monitor (ACSM) and a multi-angle absorption photometer (MAAP) were investigated at Melpitz from September 2016 to August 2017. The location of the station at the frontier between western and eastern Europe makes it the ideal place to investigate the impact of long-range transport over Europe. Indeed, the station is under the influence of less polluted air masses from westerly directions and more polluted continental air masses from eastern Europe. The OA dominated the submicron particle mass concentration and showed strong seasonal variability ranging from 39 % (in winter) to 58 % (in summer). It was followed by sulfate (15 % and 20 %) and nitrate (24 % and 11 %). The OA source identification was performed using the rolling positive matrix factorization (PMF) approach to account for the potential temporal changes in the source profile. It was possible to split OA into five factors with a distinct temporal variability and mass spectral signature. Three were associated with anthropogenic primary OA (POA) sources: hydrocarbon-like OA (HOA; 5.2 % of OA mass in winter and 6.8 % in summer), biomass burning OA (BBOA; 10.6 % and 6.1 %) and coal combustion OA (CCOA; 23 % and 8.7 %). Another two are secondary and processed oxygenated OA (OOA) sources: less oxidized OOA (LO-OOA; 28.4 % and 36.7 %) and more oxidized OOA (MO-OOA; 32.8 % and 41.8 %). Since equivalent black carbon (eBC) was clearly associated with the identified POA factors (sum of HOA, BBOA, and CCOA; R2= 0. 87), eBC's contribution to each of the POA factors was achieved using a multilinear regression model. Consequently, CCOA represented the main anthropogenic sources of carbonaceous aerosol (sum of OA and eBC) not only during winter (56 % of POA in winter) but also in summer (13 % of POA in summer), followed by BBOA (29 % and 69 % of POA in winter and summer, respectively) and HOA (15 % and 18 % of POA in winter and summer, respectively). A seasonal air mass cluster analysis was used to understand the geographical origins of the different aerosol types and showed that during both winter and summer time, PM1 (PM with an aerodynamic diameter smaller than 1 µm) air masses with eastern influence were always associated with the highest mass concentration and the highest coal combustion fraction. Since during wintertime CCOA is a combination of domestic heating and power plant emissions, the summer contribution of CCOA emphasizes the critical importance of coal power plant emissions to rural-background aerosols and its impact on air quality, through long-range transportation.

Real-world emission characteristics and inventory of volatile organic compounds originating from construction and agricultural machinery

Volatile organic compound (VOC) emissions originating from nonroad mobile sources constitute an important but uncertain source of secondary organic aerosols (SOAs) and ozone (O3). In this study, we investigated the emission factors (EFs) of 120 individual VOC species for 40 machines via gas chromatography–mass spectrometry/flame ionization detection and high-performance liquid chromatography. The results showed that the diesel-based VOC EF for the tested machines was 4.18 ± 2.55 (average ± standard deviation) g/kg fuel, dominated by alkanes (38.20 % ± 18.08 %) and oxygenated VOCs (OVOCs; 30.94 % ± 15.71 %). The machine type, rated power, emission standards, and operating conditions affected the emissions of VOCs and their components, and this effect maybe mostly depends on the fuel combustion efficiency. The VOC species were primarily distributed in the C1–C2 and C4–C6 (based on the carbon number) and B4–B6 (based on the saturated vapor concentration) intervals. Furthermore, the estimated formation potential (FP) values of SOAs and O3 from VOCs were 21.02 ± 15.57 mg/kg fuel and 15.96 ± 11.87 g/kg fuel, respectively. VOC control based on the SOA formation potential (SOAFP) and ozone formation potential (OFP) could be more effective in the mitigation of fine particulate matter (PM2.5) and O3 pollution because the top 5 species ranked by percentage contribution accounted for 83.09 % ± 9.59 % and 51.78 % ± 14.38 % of the estimated SOAFP and OFP, respectively. Finally, the emission estimates showed that the VOC emissions originating from construction and agricultural machinery in China (2020) reached 64.05 and 95.24 Gg, respectively. We provide species-specific VOC EFs and detailed emission characteristics to facilitate a comprehensive understanding of gas emissions originating from nonroad mobile sources and an update of emission inventories and atmospheric chemistry models.

Fog event is possibly a source rather than a sink of atmospheric nitrate aerosols: Insights from isotopic measurements in Nanjing, China

Nitrate is the major component of fine particle matter in recent years, and fog deposition is an important sink form of atmospheric nitrate aerosol. However, evidence shows that high relative humidity, and stable atmosphere condition may lead to the rapid increase of secondary aerosols, including nitrate. Therefore, whether fog event is a sink or a source of nitrate aerosol is still an open question. Simultaneous observations of concentration and isotopes of nitrate both in PM2.5 and fog water during fog event were conducted during a heavy fog event happened in winter of 2018 in Nanjing, a megacity sited in the Yangzi River Delta, China. Based on nine 12-h time resolution fog water samples and eleven 24-h time resolution PM2.5 samples, it was found that NO3− concentration in PM2.5 increased during the fog event (from 10.4 ± 8.6 μg m−3 to 21.2 ± 11.0 μg m−3). Compared with Δ17O–NO3- in PM2.5 before (28.4 ± 3.7‰) and after the fog event (28.6 ± 1.3‰), Δ17O–NO3- in PM2.5 during the fog event was higher (31.6 ± 1.2‰) and Δ17O–NO3- in fog water was lower (24.3 ± 1.2‰). The increased NO3− in PM2.5 during the fog event had a different formation pathway compared with NO3− in PM2.5 when there is no fog, and NO3− in fog water had another formation pathway as well. Explosive growth of NO3− in PM2.5 may come from active NO3 + HC reaction, along with happen of fog event through the reaction of NO2 with ·OH or H2O and hydrolysis of N2O5. As the fog event finished, the fog water possibly mainly settled NO3− newly generated during the fog event. It seems the fog event may be a source rather than a sink of atmospheric nitrate aerosols in this case.

Effect of Clean Heating on Carbonaceous Aerosols in PM2.5 During the Heating Period in Baoding

In order to study the effects of clean heating measures on the concentration and source of carbonaceous aerosols in PM2.5 in Baoding, we collected PM2.5 samples in Baoding during the winter heating periods of 2014 and 2019. The concentrations of OC and EC in the samples were determined by using a DRI Model 2001A thermo-optical carbon analyzer.The results showed that the average values of ρ(OC) and ρ(EC) in the heating period in 2014 were 60.92 μg·m-3 and 18.15 μg·m-3, and the average values of ρ(OC) and ρ(EC) in the heating period in 2019 were 36.63 μg·m-3 and 6.07 μg·m-3. Compared with those in 2014, the concentrations of OC and EC decreased by 39.87% and 66.56%, respectively, in 2019; the decrease in EC was larger than that in OC, and the meteorological conditions in 2019 were more severe than those in 2014, which was not conducive to the spread of pollutants.The correlation analysis and SOC estimation of OC and EC indicated that the correlation R2 of OC and EC in Baoding in 2014 and 2019 were 0.874 and 0.811, respectively, indicating that OC and EC in Baoding had relatively consistent sources. The average values of ρ(SOC) in 2014 and 2019 were 16.59 μg·m-3 and 11.31 μg·m-3, respectively, and the contribution rates to OC were 27.23% and 30.87%, respectively. This showed that in 2019, compared with that in 2014, the primary pollution decreased, but the secondary pollution increased, and the atmospheric oxidation increased.The analysis of the pollution sources of carbonaceous aerosols revealed that in 2014 and 2019 before and after the implementation of clean heating, the carbonaceous aerosols in the atmosphere were mainly from biomass combustion, coal combustion, and vehicle exhaust emissions. However, the contribution from biomass burning and coal burning decreased in 2019 compared to that in 2014. The decrease in OC and EC concentrations was attributed to the control of coal-fired and biomass-fired sources by clean heating. At the same time, the implementation of clean heating measures reduced the contribution of primary emissions to carbonaceous aerosols in PM2.5 in Baoding City.

Seasonality of Polyaromatic Hydrocarbons (PAHs) and Their Derivatives in PM2.5 from Ljubljana, Combustion Aerosol Source Apportionment, and Cytotoxicity of Selected Nitrated Polyaromatic Hydrocarbons (NPAHs).

Airborne particulate matter (PM) is a vector of many toxic pollutants, including polyaromatic hydrocarbons (PAHs) and their derivatives. Especially harmful is the fine fraction (PM2.5), which penetrates deep into the lungs during inhalation and causes various diseases. Amongst PM2.5 components with toxic potential are nitrated PAHs (NPAHs), knowledge of which is still rudimentary. Three of the measured NPAHs (1-nitropyrene (1-nP), 9-nitroanthracene (9-nA), and 6-nitrochrysene (6-nC)) were detected in ambient PM2.5 from Ljubljana, Slovenia, along with thirteen non-nitrated PAHs. The highest concentrations of pollutants, which are closely linked with incomplete combustion, were observed in the cold part of the year, whereas the concentrations of NPAHs were roughly an order of magnitude lower than those of PAHs throughout the year. Further on, we have evaluated the toxicity of four NPAHs, including 6-nitrobenzo[a]pyrene (6-nBaP), to the human kidney cell line, HEK293T. The most potent was 1-nP (IC50 = 28.7 µM), followed by the other three NPAHs, whose IC50 was above 400 or 800 µM. According to our cytotoxicity assessment, atmospheric 1-nP is the most harmful NPAH among the investigated ones. Despite low airborne concentrations of NPAHs in ambient air, they are generally considered harmful to human health. Therefore, systematic toxicological assessment of NPAHs at different trophic levels, starting with cytotoxicity testing, is necessary in order to accurately evaluate their threat and adopt appropriate abatement strategies.

Fine aerosol sources at an urban background site in the Eastern Mediterranean (Nicosia; Cyprus): Insights from offline versus online source apportionment comparison for carbonaceous aerosols

A total of 348 daily PM2.5 samples were collected at an urban background site of Nicosia, capital of Cyprus, for one-year period (October 2018–October 2019) to assess the origin and sources of fine PM at the Eastern Mediterranean, a poorly characterized area of the world.The samples were analysed for water soluble ionic species, elemental and organic carbon, carbohydrates and trace metals, the combination of which were utilized to identify pollution sources by applying Positive Matrix Factorization (PMF). Six PM2.5 sources, namely long-range transport (LRT; 38 %), traffic (20 %), biomass burning (16 %), dust (10 %), sea salt (9 %) and heavy oil combustion (7 %), were identified.Despite sampling in an urban agglomeration, the chemical fingerprint of the aerosol is largely dictated by air mass origin rather than local sources. Springtime is characterized by the most elevated particulate levels due to the southerly air masses carrying particles from the Sahara Desert. Northerlies are observed throughout the year but are predominant during summer allowing the LRT source to peak (54 % during summer). Only during winter, due to extensive use of biomass combustion for domestic heating (36.6 % during winter), local sources dominate.A co-located online PMF source apportionment of submicron carbonaceous aerosols (Organic Aerosols, OA; Black Carbon) was performed by the means of an Aerosol Chemical Speciation Monitor (for OA) and an Aethalometer (for BC) for a four-month period. The comparison between the two methodologies allowed to better assess the robustness and limitations of the two methodologies. More specifically, LRT OA and biomass burning BC apportioned by the offline PMF showed a strong consistency with the online apportioned more oxidized oxygenated OA and BCwb, respectively; cross validating these sources. On the other hand, our traffic factor may contain additional hydrocarbon-like OA and BC from fossil fuel sources other than just vehicular emissions. Finally, the offline biomass burning OA source is likely to contain both primary and secondary OA.

Marked impacts of transient conditions on potential secondary organic aerosol production during rapid oxidation of gasoline exhausts

Vehicle emission is a major source of atmospheric secondary organic aerosols (SOA). Driving condition is a critical influencing factor for vehicular SOA production, but few studies have revealed the dependence on rapid-changing real-world driving conditions. Here, a fast-response oxidation flow reactor system is developed and deployed to quantify the SOA formation potential under transient driving conditions. Results show that the SOA production factor varies by orders of magnitude, e.g., 20–1500 mg kg-fuel−1 and 12–155 mg kg-fuel−1 for China V and China VI vehicles, respectively. High speed, acceleration, and deceleration are found to considerably promote SOA production due to higher organic gaseous emissions caused by unburned fuel emission or incomplete combustion. In addition, China VI vehicles significantly reduce SOA formation potential, yield, and acceleration and deceleration peaks. Our study provides experimental insight and parameterization into vehicular SOA formation under transient driving conditions, which would benefit high time-resolved SOA simulations in the urban atmosphere.