Aerosol Components Research Articles

Emission Characteristics of Organic Carbon and Elemental Carbon in PM10 and PM2.5 from Vehicle Exhaust and Civil Combustion Fuels

To study the emission characteristics of carbonaceous aerosol in particulate matter emitted from vehicle exhaust and main civil combustion fuels, organic carbon (OC) and elemental carbon (EC) in PM10 and PM2.5 samples from vehicle sources (gasoline vehicles, light duty diesel vehicles, and heavy duty diesel vehicles), civil coal (chunk coal and briquette coal), and biomass fuels (wheat straw, wood plank, and grape branches) were collected and analyzed by using a multifunctional portable dilution channel sampler and the Model 5L-NDIR OC/EC analyzer. The results showed that there were significant differences in the proportion of carbonaceous aerosols in PM10 and PM2.5from different emission sources. The proportions of total carbon (TC) in PM10 and PM2.5 of different emission sources were 40.8%-68.5% and 30.5%-70.9%, respectively, and the OC/EC were 1.49-31.56 and 1.90-87.57, respectively. The carbon components produced by different emission sources were dominated by OC, and the OC/TC values in PM10 and PM2.5 were 56.3%-97.0% and 65.0%-98.7%, respectively. The proportions of OC in carbonaceous aerosols in PM10and PM2.5 were in the descending order of:briquette coal>chunk coal>gasoline vehicle>wood plank>wheat straw>light duty diesel vehicle>heavy duty diesel vehicle and briquette coal>gasoline car>grape branches>chunk coal>light duty diesel vehicle>heavy duty diesel vehicle, respectively. The main components of carbonaceous aerosols in PM10 and PM2.5 emitted from the various emission sources were different, and source apportionment of carbonaceous aerosols could be accurately distinguished by their ingredient composition profiles.

Drivers of High Concentrations of Secondary Organic Aerosols in Northern China during the COVID-19 Lockdowns.

During the COVID-19 lockdown in early 2020, observations in Beijing indicate that secondary organic aerosol (SOA) concentrations increased despite substantial emission reduction, but the reasons are not fully explained. Here, we integrate the two-dimensional volatility basis set into a state-of-the-art chemical transport model, which unprecedentedly reproduces organic aerosol (OA) components resolved by the positive matrix factorization based on aerosol mass spectrometer observations. The model shows that, for Beijing, the emission reduction during the lockdown lowered primary organic aerosol (POA)/SOA concentrations by 50%/18%, while deteriorated meteorological conditions increased them by 30%/119%, resulting in a net decrease in the POA concentration and a net increase in the SOA concentration. Emission reduction and meteorological changes both led to an increased OH concentration, which accounts for their distinct effects on POA and SOA. SOA from anthropogenic volatile organic compounds and organics with lower volatility contributed 28 and 62%, respectively, to the net SOA increase. Different from Beijing, the SOA concentration decreased in southern Hebei during the lockdown because of more favorable meteorology. Our findings confirm the effectiveness of organic emission reductions and meanwhile reveal the challenge in controlling SOA pollution that calls for large organic precursor emission reductions to rival the adverse impact of OH increase.

Simulation of organic aerosol, its precursors, and related oxidants in the Landes pine forest in southwestern France: accounting for domain-specific land use and physical conditions

Abstract. Organic aerosol (OA) still remains one of the most difficult components of the atmospheric aerosols to simulate, given the multitude of its precursors, the uncertainty in its formation pathways, and the lack of measurements of its detailed composition. The LANDEX (LANDes Experiment) project, during its intensive field campaign in summer 2017, gives us the opportunity to compare biogenic secondary OA (BSOA) and its precursors and oxidants obtained within and above the Landes forest canopy to simulations performed with CHIMERE, a state-of-the-art regional chemistry transport model. The Landes forest is situated in the southwestern part of France and is one of the largest anthropized forests in Europe (1×106 ha). The majority of the forest is comprised of maritime pine trees, which are strong terpenoid emitters, providing a large potential for BSOA formation. In order to simulate OA buildup in this area, a specific model configuration setup adapted to the local peculiarities was necessary. As the forest is nonhomogeneous, with interstitial agricultural fields, high-resolution 1 km simulations over the forest area were performed. Biogenic volatile organic compound (BVOC) emissions were predicted by MEGAN, but specific land cover information needed to be used and was thus chosen from the comparison of several high-resolution land cover databases. Moreover, the tree species distribution needed to be updated for the specific conditions of the Landes forest. In order to understand the canopy effect in the forest, canopy effects on vertical diffusivity, winds, and radiation were implemented in the model in a simplified way. The refined simulations show a redistribution of BVOCs with a decrease in isoprene and an increase in terpenoid emissions with respect to the standard case, both of which are in line with observations. Corresponding changes to simulated BSOA sources are tracked. Very low nighttime ozone, sometimes near zero, remains overestimated in all simulations. This has implications for the nighttime oxidant budget, including NO3. Despite careful treatment of physical conditions, simulated BSOA is overestimated in the most refined simulation. Simulations are also compared to air quality sites surrounding the Landes forest, reporting a more realistic simulation in these stations in the most refined test case. Finally, the importance of the sea breeze system, which also impacts species concentrations inside the forest, is made evident.

Nitration of Phenols by Reaction with Aqueous Nitrite: A Pathway for the Formation of Atmospheric Brown Carbon

Nitrophenols are a major component of light-absorbing atmospheric organic aerosols, commonly referred to as brown carbon (BrC). Most nitrophenol formation pathways involve reactions of phenolic compounds with OH, NO3, and NO2 in the gas phase. In this study, an aqueous nitrophenol production pathway is investigated that can proceed in the dark without apparent OH radical formation. Using high-performance liquid chromatography–mass spectrometry, we demonstrate that catechol reacts in acidic solutions with dissolved nitrite to form nitrocatechol. The rate of nitration increases significantly from pH 4.4 to pH 3.4 such that nitrocatechol is susceptible to second-generation reactions under the most acidic conditions producing chromophores that absorb in the visible region (peak at 425 nm). Increases in the N:C ratio of the reaction solution, as detected by aerosol mass spectrometry, and enhanced absorption from 300 to 500 nm of wood and peat smoke aqueous extracts exposed to nitrite suggest that this is a general nitration pathway. The atmospheric conditions under which this BrC formation process may occur are discussed.

Microphysics of liquid water in sub-10 nm ultrafine aerosol particles

Abstract. Ultrafine aerosol particles with sizes smaller than 50 nm have been shown in recent studies to serve as a large source of cloud condensation nuclei that can promote additional cloud droplet formation under supersaturation conditions. Knowledge of the microphysics of liquid water in these droplets remains limited, particularly in the sub-10 nm particle size range, due to experimental and theoretical challenges associated with the complexity of aerosol components and the small length scales of interest (e.g., difficulty of precisely sampling the liquid–air interface, questionable validity of mean-field theoretical representations). Here, we carried out molecular dynamics (MD) simulations of aerosol particles with diameters between 1 and 10 nm and characterized atomistic-level structure and water dynamics in well-mixed and phase-separated systems with different particle sizes, NaCl salinities, and pimelic acid (PML) organic surface loadings as a function of distance from the time-averaged Gibbs dividing interface or instantaneous water–air interface. We define a sphericity factor (ϕ) that can shed light on the phase-mixing state of nanodroplets, and we reveal an unexpected dependence of mixing state on droplet size. Our results also evidence an ion concentration enhancement in ultrafine aerosols, which should modulate salt nucleation kinetics in sub-10 nm droplets, and provide detailed characterization of the influence of droplet size on surface tension and on water self-diffusivity near the interface. Analysis of water evaporation free energy and water activity demonstrates the validity of the Kelvin equation and Köhler theory at droplet sizes larger than 4 nm under moderate salinities and organic loadings and the need for further extension to account for ion concentration enhancement in sub-10 nm aerosols, droplet-size-dependent phase separation effects, and a sharp decrease in the cohesiveness of liquid water in sub-4 nm droplets. Finally, we show that an idealized fractional surface coating factor (fs) can be used to categorize and reconcile water accommodation coefficients (α*) observed in MD simulations and experimental results in the presence of organic coatings, and we resolve the droplet size dependence of α*.

Determination of atmospheric aerosol components in an urban area to evaluate the air quality and identify the sources of contamination.

The need to generate objective evidence and reliable information for decision makers to improve environmental policies for a better air quality, led us to evaluate the atmospheric aerosol components in the urban area of Carabayllo, by monitoring PM2.5 and PM10 to determine mass concentration and analyzing PM10 using k 0-INAA and ICP-MS for metals quantification, ion chromatography for anions and the NIOSH method to determine organic and elemental carbon. The results obtained from mass concentration of PM2.5 and PM10 exceeded the permissible breathing annual average of WHO guidelines of 15µgm-3 and 45µgm-3, respectively, which evidence an unhealthy air quality. Likewise, using the model Positive Matrix Factorization five sources of pollutants were defined: metallurgical industry, sea salt, industrial activity, dust and non-exhaust emissions and vehicle emissions.

The impact of biomass burning emissions on aerosol concentrations and depositions in the northern South China Sea region

The impact of biomass burning (BB) emissions on concentrations and depositions of major aerosol components in the northern South China Sea (NSCS) region (105∼115°E and 15∼21°N) from December 2020 to April 2021 has been investigated using the WRF-chem model (weather research and forecasting model coupled with chemistry) in combination with aerosol composition measurement at a mountain site in the Hainan Island of China. Model comparisons with observations in Hainan demonstrated the effectiveness of WRF-chem in simulating aerosol components (PM2.5, black carbon (BC), organic matter (OM), sulfate, nitrate, and ammonium) in the NSCS region. The influences of BB emissions were significant on near-surface PM2.5, BC, and OM but nearly negligible on secondary inorganic components (i.e., sulfate, nitrate, and ammonium). The NSCS regional and period mean PM2.5, BC, and OM concentrations were 17.2 μg/m3, 0.65 μg/m3, and 6.7 μg/m3, in which 20%, 13%, and 35%, respectively, were from BB emissions. The mean PM2.5, BC, and OM deposition fluxes were 73.8 mg/m2/month, 2.9 mg/m2/month, and 29.3 mg/m2/month, respectively, and 22%, 15%, and 38% of these depositions were from BB emissions. Dry deposition dominated the removal of aerosols. For both aerosol concentrations and depositions, the influences of BB emissions exhibited evidently larger contributions in spring (March and April) than those in winter (December to February). Most of the BB emissions were from mainland Southeast Asia (MSEA), in terms of period mean, 79%, 72%, and 81% of the BB PM2.5, BB BC, and BB OM concentrations and 82%, 77%, and 83% of their depositions in the NSCS region were attributed to the MSEA region. The results of this study suggested that BB emissions have strong implications for air quality and biogeochemical cycle of the NSCS region.

Correction: Ou et al. Spatio-Temporal Variability of Aerosol Components, Their Optical and Microphysical Properties over North China during Winter Haze in 2012, as Derived from POLDER/PARASOL Satellite Observations. Remote Sens. 2021, 13, 2682

In the published article [...]

Atmospheric nanoparticles hygroscopic growth measurement by a combined surface plasmon resonance microscope and hygroscopic tandem differential mobility analyzer

Abstract. The hygroscopic growth of atmospheric aerosols plays an important role in regional radiation, cloud formation, and hence climate. Aerosol hygroscopic growth is often characterized by hygroscopic tandem differential mobility analyzers (HTDMAs), and Xie et al. (2020) recently demonstrated that hygroscopic growth measurements of a single particle are possible using a surface plasmon resonance microscope-azimuthal rotation illumination (SPRM-ARI). The hygroscopic properties of ambient aerosols are not uniform and often exhibit large relative humidity (RH) and size variabilities due to different chemical compositions and mixing states. To better understand the contribution of different aerosol components and establish a link between the apparent hygroscopic properties of single particles and bulk aerosols, we conduct combined hygroscopic growth measurements using a SPRM-ARI and an HTDMA as a case study to prove the concept (experimental information: 100–200 nm, during noontime on 28 September 2021 and 22 March 2022 in Hefei, China). According to the distinct hygroscopic growth behavior from single-particle probing using a SPRM-ARI, the individual particles can be classified into three categories defined as non-hygroscopic (NH), less hygroscopic (LH), and more hygroscopic (MH). The mean growth factor (GF) of the three categories can be utilized to reproduce the GF distribution obtained from the HTDMA measurement. The chemical compositions of individual particles from the three categories are identified to be organic carbon (OC), soot (mainly elemental carbon), fly ash, and secondary aerosols (mainly OC and sulfate), using scanning electron microscopy (SEM) with an energy-dispersive spectrometer (EDS). The coupled SPRM–HTDMA measurement suggests a size-dependent variation of aerosol chemical components, i.e., an increase of OC fraction with increasing particle sizes, which agrees reasonably well with the chemical compositions from collected aerosol samples. This likely links the hygroscopic properties of individual particles to their bulk hygroscopic growth and chemical composition.

Estimate Ground-based PM2.5 concentrations with Merra-2 aerosol components in Tehran, Iran: Merra-2 PM2.5 concentrations verification and meteorological dependence

Estimate Ground-based PM2.5 concentrations with Merra-2 aerosol components in Tehran, Iran: Merra-2 PM2.5 concentrations verification and meteorological dependence

Insights into the nitroaromatic compounds, formation, and light absorption contributing emissions from various geological maturity coals

Nitroaromatic compounds (NACs) are essential components of atmospheric organic aerosols. Coal combustion is a key source of atmospheric NACs. In this study, a triple-quadrupole liquid chromatography-mass spectrometry (LC-MS) system was used to identify ten individual NAC emitted in combustions of chunk coal and its briquette at different maturity levels. The Gaussian calculation was applied to quantify the absorption contribution of NACs to brown carbon (BrC). The emission factors (EFs) of total quantified NACs (ΣNACs) are 21.80–4429.55 μg/kg. 4-Nitrocatechol (4NC) is the most abundant NACs, accounting for 25.5–82.3 % of the ΣNACs and has the largest contribution to light absorption (0.34–29.23 %). The EFs for ΣNACs of chunk coal are 1.1–3.0 times those of its briquette, while the coal with volatile matter (VM) = 35.83 % shows the highest NAC emissions. The reaction pathway analysis demonstrates that NACs in briquette are generated through the pyrolysis of coal tar at an early stage of coal combustion, while volatile organic compounds (VOCs) that are emitted in chunk coal contribute greatly to the formations of NACs. The molecular properties analysis reveals that ΣNACs contribute 0.47–35.27 % to BrC light absorption. Anthracite coal (VM = 8.01 %) demonstrates the lowest light absorption coefficient (babs-365). Since bituminous coal (with VM = ~10 %–40 %) is popularly used for heating in rural China in winter, the results of this study could assist to evaluate the climate and environmental impacts on the NACs emission from coal combustion on a regional scale. Finally, the results highlighted that replacements of bituminous by clear fuel (such as chunk or briquette anthracite) could reduce NACs emission effectively.

Evaluation of Aerosol Optical Depth Forecasts from NOAA’s Global Aerosol Forecast Model (GEFS-Aerosols)

Abstract The NWS/NCEP recently implemented a new global deterministic aerosol forecast model named the Global Ensemble Forecast Systems Aerosols (GEFS-Aerosols), which is based on the Finite Volume version 3 GFS (FV3GFS). It replaced the operational NOAA Environmental Modeling System (NEMS) GFS Aerosol Component version 2 (NGACv2), which was based on a global spectral model (GSM). GEFS-Aerosols uses aerosol modules from the GOCART previously integrated in the WRF Model with Chemistry (WRF-Chem), FENGSHA dust scheme, and several other updates. In this study, we have extensively evaluated aerosol optical depth (AOD) forecasts from GEFS-Aerosols against various observations over a timespan longer than one year (2019–20). The total AOD improvement (in terms of seasonal mean) in GEFS-Aerosols is about 40% compared to NGACv2 in the fall and winter season of 2019. In terms of aerosol species, the biggest improvement came from the enhanced representation of biomass burning aerosol species as GEFS-Aerosols is able to capture more fire events in southern Africa, South America, and Asia than its predecessor. Dust AODs reproduce the seasonal variation over Africa and the Middle East. We have found that correlation of total AOD over large regions of the globe remains consistent for forecast days 3–5. However, we have found that GEFS-Aerosols generates some systematic positive biases for organic carbon AOD near biomass burning regions and sulfate AOD over prediction over East Asia. The addition of a data assimilation capability to GEFS-Aerosols in the near future is expected to address these biases and provide a positive impact to aerosol forecasts by the model. Significance Statement The purpose of this study is to quantify improvements associated with the newly implemented global aerosol forecast model at NWS/NCEP. The monthly and seasonal variations of AOD forecasts of various aerosol regimes are overall consistent with the observations. Our results provide a guide to downstream regional air quality models like CMAQ that will use GEFS-Aerosols to provide lateral boundary conditions.

Measurement report: Abundance and fractional solubilities of aerosol metals in urban Hong Kong – insights into factors that control aerosol metal dissolution in an urban site in South China

Abstract. Water-soluble metals are known to produce greater adverse human health outcomes than their water-insoluble forms. Although the concentrations of water-soluble aerosol metals are usually limited by atmospheric processes that convert water-insoluble metals to water-soluble forms, factors that control the solubilities of aerosol metals in different environments remain poorly understood. In this study, we investigated the abundance and fractional solubilities of different metals in size-fractionated aerosols collected at an urban site in Hong Kong and identified the factors that modulated metal solubilities in fine aerosols. The concentrations of total and water-soluble metals in fine and coarse aerosols were the highest during the winter and spring seasons due to the long-range transport of air masses by northerly prevailing winds from emission sources located in continental areas north of Hong Kong. The study-averaged metal fractional solubilities spanned a wide range for both fine (7.8 % to 71.2 %) and coarse (0.4 % to 47.9 %) aerosols, but higher fractional solubilities were typically observed for fine aerosols. Sulfate was found to be strongly associated with both the concentrations of water-soluble Cr, Fe, Co, Cu, Pb, and Mn and their fractional solubilities in fine aerosols, which implied that sulfate-driven acid processing likely played an important role in the dissolution of the water-insoluble forms for these six metals. Further analyses revealed that these strong associations were due to sulfate providing both the acidic environment and liquid water reaction medium needed for the acid dissolution process. Thus, the variability in the concentrations of water-soluble Cr, Fe, Co, Cu, Pb, and Mn and their fractional solubilities were driven by both the aerosol acidity levels and liquid water concentrations, which in turn were controlled by sulfate. These results highlight the roles that sulfate plays in the acid dissolution of metals in fine aerosols in Hong Kong. Our findings will likely also apply to other urban areas in South China, where sulfate is the dominant acidic and hygroscopic component in fine aerosols.

Quantitative Evaluation of Dust and Black Carbon Column Concentration in the MERRA-2 Reanalysis Dataset Using Satellite-Based Component Retrievals

The aerosol optical property products of Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) reanalysis dataset have been extensively investigated on a global or regional scale. However, the understanding of MERRA-2 aerosol component products on an extensive temporal and spatial scale is inadequate. Recently, the aerosol component products have been derived from the observations of Polarization and Directionality of the Earth’s Reflectances/Polarization and Anisotropy of Reflectance for Atmospheric Science coupled with observations from a Lidar (POLDER/PARASOL). This study presents a quantitative evaluation of the MERRA-2 reanalysis dust and black carbon (BC) column concentration using independent satellite-based aerosol component concentration retrievals. Both GRASP/Component and MERRA-2 reanalysis products can capture well the temporal variation in dust column concentration over the dust emission resource and downwind dust-dominated regions with the correlation coefficient (R) varying from 0.80 to 0.98. MERRA-2 reanalysis dust products present higher column concentration than GRASP/Component dust retrievals with relative differences of about 20~70%, except in the Taklamakan Desert and Bay of Bengal, where the relative differences can be negative. The differences in dust column concentration over the African dust regions are larger than that over the Asian dust regions. Similar temporal variations in BC column concentration are characterized by both GRASP/Component BC retrievals and MERRA-2 BC products with R of about 0.70~0.90, except in the North China Plain region. We should pay more caution with the regional applicability of MERRA-2 component products when large differences and high correlation coefficients are obtained simultaneously. The results are favorable for identifying the behavior of MERRA-2 reanalysis component estimation in a new view and demonstrate a practical application of the satellite-based component retrievals, which could make more contributions to the improvement of model estimation in the near future.

Kinetics of hypochlorous acid reactions with organic and chloride-containing tropospheric aerosol.

Chlorine plays an important role in tropospheric oxidation processes, in both marine and continental environments. Although modeling studies have explored the importance of halogen chemistry, uncertainty remains in associated chemical mechanisms and fundamental kinetics parameters. Prior kinetics measurements of multiphase halogen recycling reactions have been largely performed with dilute, bulk solutions, leaving unexplored more realistic chemical systems which have high solute concentrations and are internally mixed with both halide and organic components. Here, we address the multiphase kinetics of gaseous HOCl using an aerosol flow tube and aerosol mass spectrometer to study its reactions with particulate chloride, using atmospherically relevant particle acidity, solute concentrations, and ionic strength. We also investigate the chemistry that results when biomass burning (BB) aerosol components and chloride are internally mixed. Using pH-buffered deliquesced particles, we show that the rate constant for reaction of dissolved HOCl with H+ and Cl- at high relative humidity (RH) (80-85%) is within a factor of two of the literature value for bulk phase conditions. However, at lower RH values (60-70%) where the particles are considerably more concentrated, the rate constant for chloride loss from the particles is an order of magnitude higher. For pure organic compounds commonly found in biomass burning (BB) aerosol, such as coniferaldehyde, salicylic acid and furfural, an increase in the aerosol chlorine content occurs with HOCl exposure, indicating the formation of organochlorine species. Together, these independent findings explain results for internally mixed aerosol particles with both chloride and BB components present where we observed behavior consistent with both chloride loss and organochlorine formation occurring simultaneously upon HOCl exposure. Our results indicate that chlorine recycling via HOCl uptake by chloride-containing particles will occur in the atmosphere efficiently over a wide range of RH conditions, even when reactive organic compounds are present in the same particles as chloride. Simultaneously, formation of organochlorine compounds, which are commonly toxic, is likely occurring when reactive organic components are present.

Enrichment of Organic Acids in Fine Particles Over a Megacity in South China

AbstractOrganic acids are abundant aerosol components that impact the hygroscopicity and multiphase processes of particulate matter, yet their changing compositions and sources are poorly understood. In this study, filter‐based PM2.5 samples were collected concurrently at three sites (urban, rural, and coastal) during the summer and winter of 2018 in the megacity Guangzhou, south China, to determine organic acids including C9–C32 fatty acids, C4–C10 dicarboxylic acids, and aromatic acids. On average, the total concentrations of the speciated organic acids were higher in winter than in summer, and were the highest at the urban site. Compared to observations at the same sites in winter 2009, average concentrations of organic acids in winter 2018 increased by 35.0%, 66.0%, and −3.2% at the urban, rural and coastal sites, while their fractions in organic matter (OM) increased by approximately 261.5%, 266.7%, and 61.1%, and their fractions in PM2.5 increased by approximately 318.2%, 308.7%, and 221.1%, respectively. Source apportionment of organic acids revealed that cooking emission and vehicle exhaust were the major sources at the urban site, plant wax and vehicle exhaust were the two largest sources at the rural site with substantial contributions from biomass burning in winter, while vehicle exhaust and ship emission were the two major sources at the coastal site. Less contributions from secondary production were retrieved in winter 2018 than in winter 2009, and the enrichment of organic acids in PM2.5 or OM was attributed to their elevated primary emissions from vehicles and ships, cooking, and plant wax.

Quantification and identification of airborne small microplastics (

The atmosphere is a significant pathway for distributing plastic particles and other micro-litter particles from their sources to other environmental compartments. There is a big gap regarding the standardized method for the quantification and identification of airborne microplastics (MPs), especially those in the range of 5–100 μm (small microplastics, SMPs) and airborne micro-litter components (MLCs), i.e., plastic additives, natural fibers and non-plastics synthetic fibers. This study aimed to develop and optimize a pre-treatment method (i.e., elutriation, oleoextraction, and purification) to extract SMPs and MLCs simultaneously from urban aerosol samples. The quantification and simultaneous chemical characterization were performed via Micro-FTIR. The method developed was then applied to two samples from different seasons, i.e., summer and late fall – winter. Micro-litter particles followed the Poisson distribution, and the fiducial limit (confidence interval) was calculated accordingly. Non-parametric statistical tests were performed to evaluate significant differences among the samples. The most abundant plastic polymers were polyethylene (HDPE) and polytetrafluoroethylene (PTFE). Among MLCs, flame retardants, UV filters, stabilizers, and rayon were identified. The results of this study will contribute significantly to establishing standardized and accredited methods to quantify and identify airborne SMPs and MLCs.

Aerosol Characterization with Long-Term AERONET Sun-Photometer Measurements in the Naples Mediterranean Area

We report on the characterization of columnar aerosol optical and microphysical properties in the Naples Mediterranean area over a period of five years by the ground-based sun–sky–lunar photometer operating at our observational station in the frame of the AERONET network. Statistical and climatological analyses of daily mean values of aerosol optical depth at 440 nm (AOD440) and Ångström exponent at 440/870 nm (α440/870) allowed for highlighting their typical seasonal behavior. In particular, we observe higher mean values of the AOD440 during summer or spring, which are consistent with an increased frequency of both Saharan dust transport events and biomass burning episodes affecting the measurement area in these periods of the year. Conversely, α440/870 does not show any typical seasonal trend. In order to gain information on the different aerosol contributions along the atmospheric column, the frequency distributions of AOD440 and α440/870 were analyzed and fitted by a superposition of Gaussian functions. The most populated modes are centered at α440/870 = 1.26 ± 0.07 and AOD440 = 0.16 ± 0.01. These values are associated with continental polluted aerosol mixed with sea salt aerosol and correspond to the background conditions typically observed in clear atmospheric conditions. Daily size distributions averaged over each month highlight that the fine aerosol component always prevails over the coarse fraction, except for the few months in which Saharan dust events are particularly frequent. Finally, the mean value of the SSA at 440 nm resulted as 0.94 ± 0.05, while the refractive index real and imaginary part were 1.47 ± 0.07 and (6.5 ± 0.2) × 10−3, respectively. These values are in agreement with those observed in other Mediterranean sites located in Southern Italy, evidencing a rather characteristic feature of the geographical region.

A sampling of environmental data, and its presentation, from a multi-role U.S. coast guard aircraft

Abstract This work presents a summary of environmental data from 3600 h of data collected during operations of a U.S. Coast Guard HC-130H aircraft performing its routine missions over a five-year period. The aircraft operated from multiple U.S. and deployed locations during the data collection period in the tropical and mid-latitudes at altitudes up to 8.5 km (28 kft). The aircraft collected pressure, temperature and humidity data during the period. No aerosol components were sampled (chlorides, sulfur dioxide, etc.). While there was no Time of Wetness sensor, the ISO 9223 definition is used for the present work as an estimator. These data are presented in the context of research into corrosion and environmental severity, or the potential conditions for it. About 40% of the data were collected while the aircraft was parked on the ground at various based and deployed locations. The purpose of this work is to present and summarize the flight data as an aid in providing some context for future research into environmental effects as they relate to both corrosion and environmentally assisted cracking (EAC) of aircraft structure, and perhaps for comparisons with existing or future datasets from aircraft having other missions. Prediction models need realistic, real-world inputs, such as those presented here. An example for the use of these data in corrosion prediction based on the ISO 9223 international standard is presented. Perhaps not surprisingly, these data show that, for this aircraft, conditions most favorable to corrosion occurred while the aircraft was on the ground.

In Vitro Toxicological Investigation and Risk Assessment of E-Cigarette Aerosols Based on a Novel Solvent-Free Extraction Method.

Cigarettes, potentially safer alternatives to combustible cigarettes, have been reported to increase the health risk for long-term users, so accumulating information about their potential toxicity is of great concern. However, toxicological evaluations of e-cigarette aerosols are limited, which may be attributed to the lack of a simple and efficient extraction method. Here, we developed a high-speed centrifugal method for extracting e-cigarette aerosol collected mass (ACM) and prepared ACM samples of 26 representative e-cigarettes, and 10 samples were further selected based on their cytotoxicity for systematic toxicological assessments. The average extraction efficiency of ACM, primary aerosol components, and typical carbonyls exceeded 85%. The toxicological evaluation showed that the IC50 value range of e-cigarettes for cytotoxicity was 2-52 mg/mL ACM, all e-cigarettes can induce the risk of DNA damage, mitochondrial depolarization, and c-Jun-related signal disturbances; most e-cigarettes significantly caused disturbance of oxidative stress balance. E-cigarettes with higher cytotoxicity appeared to cause a higher degree of damage, while no e-cigarette promoted mutagenicity and cytochrome c release. The toxicity difference among e-cigarettes using nicotine equivalent was significantly lower than that of ACM. This study provides a novel extraction method and a comprehensive in vitro toxicity risk profile of e-cigarette aerosols.