Coarse Mode Research Articles

The Scattering and Absorption Coefficients of Atmospheric Soot in the Hygroscopicity of Urban Aerosols

Aerosols are microscopic solid or liquid particles suspended in the atmosphere that have an impact on the Earth's radiative balance. This paper modeled and investigates the effect of scattering and absorption coefficients along with their respective hygroscopicity of atmospheric soot using extracted data from Optical Properties of Aerosols and Clouds (OPAC) incorporated with Fortran at spectral range of 0.25 to 1.00 m for eight different relative humidities (RHs) (0, 50, 70, 80, 90, 95, 98 and 99%). The fine – mode and coarse – mode aerosol size distribution were also investigated. The particle number densities of soot were varied as 110,000 120,000 and 130,000 cm-3 while the water soluble and insoluble components were kept constant. The scattering coefficient decreases with RHs and also with wavelength in the form of power law at all RHs. The absorption coefficient increases with addition of soot, reflecting warming effect. In this study, it was observed that there is a pronounced hygroscopicity growth as from 95-99% RHs. The Ångström exponent decreases with increase in RHs for the case of scattering coefficient but varies for absorption coefficient; the curvature reveals the presence of both fine and coarse mode particles. The results of the turbidity coefficient (????) based on the scattering coefficient indicated that the atmosphere is relatively clear and hazy while the absorption coefficient indicated that the atmosphere is relatively clear at 0 – 99% relative humidity. The results in this study revealed that the coefficient of determination, ???? 2 > 96% for all the models (1 – 3).

Pre-filter analysis for retrieval of microphysical particle parameters: a quality-assurance method applied to 3 backscatter (β) +2 extinction (α) optical data taken with HSRL/Raman lidar.

We analyze the solution space of 3β+2α optical data inferred from lidar measurements, i.e., backscatter coefficients at three wavelengths and extinction coefficients at two wavelengths. These optical data are governed by microphysical parameters that can be expressed in terms of particle size distribution, effective radius, and complex refractive index (CRI). In our analysis, we consider two scenarios of the solution space. First, it can be expressed in terms of monomodal particle size distributions represented either by fine modes or by coarse modes. Secondly, the particle size distributions contain a fine mode as well as a coarse mode. Consideration of both scenarios and different values of the effective radius and CRI allows us to find synthetic 3β+2α optical data and corresponding intensive parameters (IPs) such as lidar ratios, backscatter- and extinction-related Ångström exponents at the available measurement wavelengths. Based on interdependencies between synthetic IPs and various microphysical properties, the qualitative and quantitative criteria for the optical data quality-assurance tool are developed. We derive the conditions of smoothness, closeness, convergence, and stability of the solution space for the quantitative criteria to test the quality of the 3β+2α optical data. Our novel methodology, to the best of our knowledge, can be used not only for particles of spherical shape, but also for cases in which particles are irregularly shaped. Another strength of our methodology is that it also works for the case of a size-dependent and wavelength-dependent CRI. We show the potential of this methodology for a measurement case from the ORACLES campaign. Data were taken with NASA Langley's airborne HSRL-2 instrument on September 24, 2016.

Characterization of Particle Size Distributions and Water-Soluble Ions in Particulate Matter Measured at a Broiler Farm

The chemical composition and size distribution of particulate matter produced at broiler poultry houses is not well understood, so this is a novel study to understand the particulate size distributions at a poultry house as well as the ionic composition of the particulate matter using real-time methods. Two optical particle counters provided particle size distributions inside and outside the house. An ambient ion monitor and a particle-in-liquid sampler analyzed the ionic chemical composition of the particulate matter in the house while a scanning mobility particle sizer provided size information in the nanoparticle range. Ammonia concentrations in the house were measured using a chemical sensor. Ammonia concentrations in the house were consistently in the lower part of the per million range 2–20 ppm. The optical particle counter and ion chromatography measurements both showed a strong diurnal variation of particulate matter concentration in the house throughout the study, associated with the lights being on and animal activity. Particulate mass concentration inside the house was dominated by coarse mode particles as opposed to the outdoor sampler which showed much smaller sizes. A few new particle formation and growth events were observed in the house. Ionic constituents detected by chromatography made up a small fraction of the overall mass concentration. The composition of the ionic constituents was similar for most of the study with typical ions being ammonium, sodium, potassium, chloride, sulfate, nitrate, nitrite, phosphate, and several carboxylates (formate, acetate, propionate, and butyrate.) At the end of the study, bromide was also detected during the last several days. Overall, we determined that the ionic components of the particulate matter formed through secondary particle formation was small, but also that some ionic constituents can be associated with management practices.

Comparison of aerosol optical properties over Lumbini, Pokhara and Langtang-Base Camp


 
 
 
 The comparative study of aerosol optical properties at different tourist places in Nepal has been performed. Lumbini, Pokhara and Langtang-Base Camp (BC) were the places chosen for observation. Aerosols are made up of a variety of airborne particles both fine and coarse and are most prevalent in urban industrial Areas. The data was collected from AERONET websites between 2017 and 2019 for each of the locations. The ranges of AOD over Pokhara and Langtang-BC were discovered to be lower (0.1 and 0.01) and the maximum and minimum values of AOD (675 nm) in Lumbini occurred predominantly in winter and summer monsoon respectively. The causes of the highest AOD levels were land clearing for crop cultivation and vegetation fires which were then followed by biomass burning for heating purposes and pollution from brick kilns, industry and vehicles. AOD, angstrom exponent (α and β) and Visibility are distinct from typical seasonal variations. The total AE fluctuations show that a combination of fine and coarse mode particles as well as anthropogenic aerosols made up the majority of the aerosol loading during the research period. Visibility was inversely related to the turbidity coefficient (β). Three times as much visibility was discovered over Langtang-BC as compared to Lumbini and Pokhara. Over these three locations, precipitable water peaked in the summer and dropped in the winter. These three sites seasonal changes are found to be distinct for each parameter.
 
 
 

Modelling wintertime sea-spray aerosols under Arctic haze conditions

Abstract. Anthropogenic and natural emissions contribute to enhanced concentrations of aerosols in the Arctic winter and early spring, with most attention being paid to anthropogenic aerosols that contribute to so-called Arctic haze. Less-well-studied wintertime sea-spray aerosols (SSAs) under Arctic haze conditions are the focus of this study, since they can make an important contribution to wintertime Arctic aerosol abundances. Analysis of field campaign data shows evidence for enhanced local sources of SSAs, including marine organics at Utqiaġvik (formerly known as Barrow) in northern Alaska, United States, during winter 2014. Models tend to underestimate sub-micron SSAs and overestimate super-micron SSAs in the Arctic during winter, including the base version of the Weather Research Forecast coupled with Chemistry (WRF-Chem) model used here, which includes a widely used SSA source function based on Gong et al. (1997). Quasi-hemispheric simulations for winter 2014 including updated wind speed and sea-surface temperature (SST) SSA emission dependencies and sources of marine sea-salt organics and sea-salt sulfate lead to significantly improved model performance compared to observations at remote Arctic sites, notably for coarse-mode sodium and chloride, which are reduced. The improved model also simulates more realistic contributions of SSAs to inorganic aerosols at different sites, ranging from 20 %–93 % in the observations. Two-thirds of the improved model performance is from the inclusion of the dependence on SSTs. The simulation of nitrate aerosols is also improved due to less heterogeneous uptake of nitric acid on SSAs in the coarse mode and related increases in fine-mode nitrate. This highlights the importance of interactions between natural SSAs and inorganic anthropogenic aerosols that contribute to Arctic haze. Simulation of organic aerosols and the fraction of sea-salt sulfate are also improved compared to observations. However, the model underestimates episodes with elevated observed concentrations of SSA components and sub-micron non-sea-salt sulfate at some Arctic sites, notably at Utqiaġvik. Possible reasons are explored in higher-resolution runs over northern Alaska for periods corresponding to the Utqiaġvik field campaign in January and February 2014. The addition of a local source of sea-salt marine organics, based on the campaign data, increases modelled organic aerosols over northern Alaska. However, comparison with previous available data suggests that local natural sources from open leads, as well as local anthropogenic sources, are underestimated in the model. Missing local anthropogenic sources may also explain the low modelled (sub-micron) non-sea-salt sulfate at Utqiaġvik. The introduction of a higher wind speed dependence for sub-micron SSA emissions, also based on Arctic data, reduces biases in modelled sub-micron SSAs, while sea-ice fractions, including open leads, are shown to be an important factor controlling modelled super-micron, rather than sub-micron, SSAs over the north coast of Alaska. The regional results presented here show that modelled SSAs are more sensitive to wind speed dependence but that realistic modelling of sea-ice distributions is needed for the simulation of local SSAs, including marine organics. This study supports findings from the Utqiaġvik field campaign that open leads are the primary source of fresh and aged SSAs, including marine organic aerosols, during wintertime at Utqiaġvik; these findings do not suggest an influence from blowing snow and frost flowers. To improve model simulations of Arctic wintertime aerosols, new field data on processes that influence wintertime SSA production, in particular for fine-mode aerosols, are needed as is improved understanding about possible local anthropogenic sources.

Size‐Resolved Atmospheric Phosphorus in Shanghai: Seasonal Variations, Sources and Dry Deposition

AbstractAtmospheric deposition is an important source for the P biological cycle, especially for P‐limited ecosystems. In the present study, 48 hr size‐segregated aerosol samples were collected at an urban site in Shanghai for one year from May 2019 to June 2020. Total phosphorus (TP) presented a bimodal distribution in four seasons, which was mainly contributed by mineral dust in the coarse mode, and was related to anthropogenic and combustion emissions in the fine mode. Dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP) presented a bimodal distribution in spring and summer, and a unimodal distribution dominated by a fine mode in autumn and winter. Size distributions and correlation analysis showed that DIP in the fine and coarse modes originated from the acid processing of SO42‐ and NO3−, respectively, while DOP was mainly from biomass burning emissions. Positive Matrix Factor analysis showed that phosphorus (P) in atmospheric aerosols in Shanghai was mainly contributed by four sources, including crustal sources, sea‐salt, industry emissions and fossil fuel combustion, and biomass burning. Industry emissions and fossil fuel combustion, as well as biomass burning were important sources of TP in all particle sizes (50%–65%). Biomass burning was the most important source of DOP (>50%). The total deposition flux of total dissolved phosphorus (TDP) calculated based on the size‐weighted deposition velocity model averaged 75.2 ± 17.4 μg/m2/d. Assuming that all of TDP is bioavailable, TDP deposition can create a primary production of 8.0 mg C/m2/d, which can support 1.3%–4.4% of the new production in the East China Sea.

Influence of vehicular emissions and meteorological factors towards anionic surfactants in the urban atmospheric aerosol of Kuala Lumpur, Malaysia

This study aimed to determine the influence of vehicular emissions and meteorological factors on the level of surfactants in urban atmospheric aerosol from Kuala Lumpur city center, Malaysia. Aerosol samples were collected using a high-volume sampler equipped with the cascade impactor to separate fine mode (< 1.5 µm) and coarse mode (> 1.5 µm) particles. Besides, the exhaust particulate matter from various diesel and petrol vehicles was collected using a soft brush during dry weather. Colorimetric analysis was performed to determine the concentration of anionic surfactants as methylene blue active substances (MBAS), and the absorption was determined by using a UV spectrophotometer at a wavelength of 650 nm. Correlation analysis was conducted to determine the influence of vehicular emissions (NOx, SO2, CO and O3), and exhaust particulate matter on the level of surfactants. Results showed that surfactants as MBAS in fine particles showed the dominant values. Correlation analysis showed that the MBAS was positively correlated with NOx (p <0.05) and SO2 (p <0.01), and negatively correlated with O3 (p <0.01), which indicated that the traffic-related air pollutant may influence the anionic surfactants level. It is supported by the high level of MBAS in diesel exhaust particulate matter, particularly from the construction machinery, followed by lorries and buses.

The observational evidence of association between types of aerosol mode-cloud-precipitation interaction over Iran

The present study quantifies for the first time the statistical relationship between aerosol properties with Cloud microphysical Properties (CPs), and consequently effect on precipitation over Iran. The daily means of Aerosol Optical Depth (AOD), Angstrom Exponent (AE), and CP including Cloud Fraction (CF), Cloud Top Temperature (CTT), Cloud Top Pressure (CTP), Cloud Optical Thickness (COT), and Cloud Effective Radius (CER) were obtained from the MODerate resolution Imaging Spectroradiometer (MODIS). The precipitation was retrieved from Tropical Rainfall Measuring Mission (TRMM) during 2003–2019 for 156 1 × 1 geographical degree grid-points over Iran. The different types of aerosols including the dust and fine aerosols were separated using the AOD and AE values for each season. We identified grid points, which had statistically significant correlation (at the 5% level) between aerosol modes and at least one of CPs, the precipitation and one of CPs, and between the precipitation and aerosols modes, at the same time. With this approach, we identified 10 points showing a statistically significant relationship between AOD, CPs, and precipitation, stimulatingly. For instance, at a point in the southwest of Iran, the correlation coefficient between the AOD with precipitation (r = 0.54), AOD with CTP (r = −0.51), and precipitation with CTP (r = −0.61) were statistically significant simultaneously. Based on statistical calculations, the relationship between precipitation and AOD (for 10 points) is often positive, which indicates the positive effect of aerosols on precipitation. However, in two points, the relationship between precipitation and AOD is negative, and subsequently significant. In addition, a negative correlation coefficient is also observed between CTT and CTP with AOD, as well as a positive relationship between AOD and COT for both fine (black carbon) and coarse mode (desert dust) of aerosols over Iran. Due to the lack of ground station data in Iran, this study can serve as a starting point to better understanding the complex, and uncertain response to cloud, radiation and precipitation to aerosol over arid region of Iran.

Variations of inhalation risks during different heavy pollution episodes based on 3-year measurement of toxic components in size-segregated particles

Toxic metals (TMs) and polycyclic aromatic hydrocarbons (PAHs) in size-segregated particles during common days (CD) and different heavy pollution (HP) episodes were measured during 2018–2021 in a Chinese megacity. The Multiple Path Particle Dosimetry Model (MPPD) was performed to estimate deposition efficiency, and then inhalation risks in the human pulmonary region during different types of HP were assessed and compared. The higher pulmonary deposition efficiency of PAHs and TMs during all types of HP than those during CD was confirmed. The accumulative incremental lifetime cancer risk (ILCR) of different HP were 2.42 × 10−5, 1.52 × 10−5, 1.39 × 10−5, 1.30 × 10−5 and 2.94 × 10−6 for HP4 (combustion sources HP), HP1 (ammonium nitrate HP), HP5 (mixed sources HP), HP3 (resuspended dust HP) and HP2 (ammonium sulfate HP), respectively. The accumulative hazard quotient (HQ) during different HP episodes decreased in the order of HP4 (0.32) > HP3 (0.24) > HP1 (0.22) > HP5 (0.18) > HP2 (0.05). The inhalation risks were dominated by Ni and Cr, what's more, the HQ of Ni and ILCR of Cr during the five HP episodes shared a similar size distribution pattern. However, the characteristic components during different HP episodes and their size distributions of them were distinctive. The size distribution of inhalation risks of the related components (Ni, Cr, BaP, and As) from the combustion process during HP4 peaked at fine mode (0.65–2.1 μm). The size distribution of inhalation risks of the dust-related components (Mn and V) and the components (As and BaP) that are likely to volatilize and re-distribution peaked at coarse mode (2.1–3.3 μm) during HP3. Notably, Mn and Co as catalysts at fine mode could increase the degree of secondary formation and toxicity.

Modelling the European wind-blown dust emissions and their impact on particulate matter (PM) concentrations

Abstract. Wind-blown dust (WBD) emitted by the Earth’s surface due to sandblasting can potentially have important effects on both climate and human health via interaction with solar and thermal radiation, reducing air quality. Apart from the main dust “centres” around the world, like deserts, dust can be emitted from partly vegetated mid- and high-latitude areas like Europe if certain conditions are suitable (strong winds, bare soil, reduced soil moisture, etc.). Using a wind-blown dust model (WBDUST) along with a chemical transport model (Comprehensive Air-quality model with Extensions, CAMx) coupled to a regional climate model (Weather Research and Forecasting, WRF), this study is one of the first to provide a model-based estimate of such emissions over Europe as well as the long-term impact of WBD emissions on the total particulate matter (PM) concentrations for the 2007–2016 period. We estimated average WBD emissions of about 0.5 and 1.5 Mgyr-1km-2 in fine and coarse modes. Maximum emissions occur over Germany, where the average seasonal fine- and coarse-mode emission flux can reach 0.5 and 1 gs-1km-2, respectively. Large variability is seen in the averaged daily emissions with values of up to 2 gs-1km-2 for the coarse-mode aerosol on selected days. The WBD emissions increased the modelled winter PM2.5 and PM10 concentrations by up to 10 and 20 µg m−3, respectively, especially over Germany, where the highest emissions occur. The impact on other seasons is lower. Much higher impacts are modelled, however, on selected days when occasionally the urban PM2.5 and PM10 concentrations are increased by more than 50 and 100 µg m−3. The comparison with measurements revealed that if WBD is considered, the summer biases are reduced; however, the winter PM is overestimated even more greatly (so the bias increases). We identified a strong overestimation of the modelled wind speed (the maximum daily wind is almost 2 times higher in WRF than the measured ones) suggesting that WBD emissions are also overestimated – hence the enhanced winter PM biases. Moreover, we investigated the secondary impacts of the crustal composition of fine WBD particles on secondary inorganic aerosol (SIA): sulfates (PSO4), nitrates (PNO3) and ammonium (PNH4). Because the water pH value, and thus the uptake of the gaseous precursors of SIA, is perturbed and because the increased aerosol surface serves as an oxidation site, we modelled seasonal PSO4 and PNO3 concentrations increased by up to 0.1 µg m−3 and PNH4 ones decreased by up to −0.05 µg m−3, especially during winter. In terms of average daily impact, these numbers can, however, reach much larger values of up to 1–2 µg m−3 for sulfates and nitrates, while the decrease in ammonium due to WBD can reach −1 µg m−3 on selected days. The sensitivity test on the choice of the inorganic equilibrium model (ISORROPIA vs. EQuilibrium Simplified Aerosol Model V4, EQSAM) showed that if EQSAM is used, the impact on SIA is slightly stronger (by a few 10 %) due to larger number of cations considered for water pH in EQSAM. Our results have to be regarded as a first estimate of the long-term WBD emissions and the related effects on PM over Europe. Due to the strong positive wind bias and hence strong WBD emissions, we should consider these results as an upper bound. More sensitivity studies involving the impact of the driving meteorological fields, WBD model choice and the input data used to describe the land surface need to be carried out in future to better constrain these emissions.

Characterization of free L- and D-amino acids in size-segregated background aerosols over the Ross Sea, Antarctica

The study of airborne chemical markers is crucial for identifying sources of aerosols, and their atmospheric processes of transport and transformation. The investigation of free amino acids and their differentiation between the L- and D- enantiomers are even more important to understand their sources and atmospheric fate. Aerosol samples were collected with a high-volume sampler with cascade impactor at Mario Zucchelli Station (MZS) on the coast of the Ross Sea (Antarctica) for two summer campaigns (2018/19 and 2019/20). The total mean concentration of free amino acids in PM10 was 4 ± 2 pmol m-3 for both campaigns and most of free amino acids were distributed in fine particles. The coarse mode of airborne D-Alanine and dimethylsufoniopropionate in seawater showed a similar trend during both Antarctic campaigns. Thus, the study of D/L Ala ratio in fine, coarse and PM10 fractions indicated the microlayer as the local source. This paper demonstrated that free amino acids follow the trend of DMS and MSA release occurred in the Ross Sea, confirming their applicability as markers for phytoplankton bloom also in paleoclimatic studies.

The Role of Midlatitude Cyclones in the Emission, Transport, Production, and Removal of Aerosols in the Northern Hemisphere

AbstractWe examine the distribution of aerosol optical depth (AOD) across 27,707 northern hemisphere (NH) midlatitude cyclones for 2005–2018 using retrievals from the Moderate Resolution Spectroradiometer (MODIS) sensor on the Aqua satellite. Cyclone‐centered composites show AOD enhancements of 20%–45% relative to background conditions in the warm conveyor belt (WCB) airstream. Fine mode AOD accounts for 68% of this enhancement annually. Relative to background conditions, coarse mode AOD is enhanced by more than a factor of two near the center of the composite cyclone, co‐located with high surface wind speeds. Within the WCB, MODIS AOD maximizes in spring, with a secondary maximum in summer. Cyclone‐centered composites of AOD from the Modern Era Retrospective analysis for Research and Applications, version 2 Global Modeling Initiative (M2GMI) simulation reproduce the magnitude and seasonality of the MODIS AOD composites and enhancements. M2GMI simulations show that the AOD enhancement in the WCB is dominated by sulfate (37%) and organic aerosol (25%), with dust and sea salt each accounting for 15%. MODIS and M2GMI AOD are 60% larger in North Pacific WCBs compared to North Atlantic WCBs and show a strong relationship with anthropogenic pollution. We infer that NH midlatitude cyclones account for 355 Tg yr−1 of sea salt aerosol emissions annually, or 60% of the 30–80°N total. We find that deposition within WCBs is responsible for up to 35% of the total aerosol deposition over the NH ocean basins. Furthermore, the cloudy environment of WCBs leads to efficient secondary sulfate production.

Precipitation frequency controls nitrogenous aerosol in a tropical coastal city and its implications for plant carbon sequestration

The concentration of nitrogenous aerosols is influenced by air mass transition, local meteorological conditions, local emissions, and the wet removal effect driven by precipitation. Deposited nitrogenous aerosols influence nitrogen availability in the canopy, affecting the amount of plant carbon sequestration. However, the factors controlling nitrogenous aerosol concentrations and their implications for plant carbon sequestration remain unclear. In this study, multiple stable nitrogen isotopes in atmospheric aerosols (δ15N-TN, δ15N–NO3–, and δ15N–NH4+) and rainwater (rainwater δ15N–NO3– and rainwater δ15N–NH4+) in one-year observations were analyzed to explore the main factors controlling nitrogenous aerosol concentrations. The results showed that NO3− and NH4+ were the major components of TN, and their concentrations in seasonal patterns were sensitive to frequent rainfall rather than local emissions or external contributions. The concentrations of nitrogenous aerosols were negatively correlated with precipitation frequency, indicating that increased precipitation frequency induced low concentrations of nitrogenous aerosols. Moreover, the positive matrix factorization (PMF) analysis showed that coarse mode NO3− was generated in the wet season but not in the dry season, reflecting the removal of precipitation. With the increased precipitation frequency from May to July, 42.4% of aerosol NO3− was scavenged into rainwater, indicated by the variations in the δ15N values of nitrogenous aerosols and rainwater. This result prompted us to calculate the loss of 12.1 ± 3.9 Gg carbon/yr plant carbon sequestration. Our study suggests that nitrogenous aerosols are captured by the high precipitation frequency in tropical areas, decreasing nitrogen availability in the canopy, which might decrease plant carbon sequestration.

Urban particulate water-soluble organic matter in winter: Size-resolved molecular characterization, role of the S-containing compounds on haze formation

Water-soluble organic matter (WSOM), as a group of ubiquitous components in atmospheric PM, plays a crucial role in global climate change and carbon cycle. In this study, the size-resolved molecular characterization of WSOM in the range of 0.010–18 μm PM was studied to gain insights into their formation processes. The CHO, CHNO, CHOS, CHNOS compounds were identified by the ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry in ESI source mode. A bimodal pattern of the PM mass concentrations was found in the accumulation and coarse mode. The increasing mass concentration of PM was mainly attributed to the growth of large-size PM with the occurrence of haze. Both Aiken-mode (70.5–75.6 %) and coarse-mode (81.7–87.9 %) particles were proven the main carriers of the CHO compounds, the majority of which were indicated to be the saturated fatty acids and their oxidized derivatives. The S-containing (CHOS and CHNOS) compounds in accumulation-mode (71.5–80.9 %) increased significantly in hazy days, where organosulfates (C11H20O6S, C12H22O7S) and nitrooxy-organosulfates (C9H19NO8S, C9H17NO8S) were confirmed in majority. The S-containing compounds in accumulation-mode particle with high oxygen content (6–8 oxygen atoms), unsaturation degree (DBE < 4), and reactivity could facilitate the particle agglomeration and accelerate the haze formation.

Relationship between the sub-micron fraction (SMF) and fine-mode fraction (FMF) in the context of AERONET retrievals

Abstract. The sub-micron (SM) aerosol optical depth (AOD) is an optical separation based on the fraction of particles below a specified cutoff radius of the particle size distribution (PSD) at a given particle radius. It is fundamentally different from spectrally separated FM (fine-mode) AOD. We present a simple (AOD-normalized) SM fraction versus FM fraction (SMF vs. FMF) linear equation that explains the well-recognized empirical result of SMF generally being greater than the FMF. The AERONET inversion (AERinv) products (combined inputs of spectral AOD and sky radiance) and the spectral deconvolution algorithm (SDA) products (input of AOD spectra) enable, respectively, an empirical SMF vs. FMF comparison at similar (columnar) remote sensing scales across a variety of aerosol types. SMF (AERinv-derived) vs. FMF (SDA-derived) behavior is primarily dependent on the relative truncated portion (εc) of the coarse-mode (CM) AOD associated with the cutoff portion of the CM PSD and, to a second order, the cutoff FM PSD and FM AOD (εf). The SMF vs. FMF equation largely explains the SMF vs. FMF behavior of the AERinv vs. SDA products as a function of PSD cutoff radius (“inflection point”) across an ensemble of AERONET sites and aerosol types (urban-industrial, biomass burning, dust, maritime and a mixed class of Arctic aerosols). The overarching dynamic was that the linear SMF vs. FMF relation pivots clockwise about the approximate (SMF, FMF) singularity of (1, 1) in a “linearly inverse” fashion (slope and intercept of approximately 1−εc and εc) with increasing cutoff radius. SMF vs. FMF slopes and intercepts derived from AERinv and SDA retrievals confirmed the general domination of εc over εf in controlling that dynamic. A more general conclusion is the apparent confirmation that the optical impact of truncating modal (whole) PSD features can be detected by an SMF vs. FMF analysis.

Understanding population exposure to size-segregated aerosol and associated trace elements during residential cooking in northeastern India: Implications for disease burden and health risk

Mass-size distribution of respirable aerosol and 13 associated trace elements (TEs) were investigated in rural kitchens using liquefied petroleum gas (LPG), firewood and mixed biomass fuels across three northeastern Indian states. The averaged PM10 (particulate matter with aerodynamic diameter ≤ 10 μm) and ΣTE concentrations were 403 and 30 μg m−3 for LPG, 2429 and 55 μg m−3 for firewood, and 1024 and 44 μg m−3 for mixed biomass-using kitchens. Mass-size distributions were tri-modal with peaks in the ultrafine (0.05–0.08 μm), accumulation (0.20–1.05 μm), and coarse (3.20–4.57 μm) modes. Respiratory deposition, estimated using the multiple path particle dosimetry model, ranged from 21 % to 58 % of the total concentration across fuel types and population age categories. Head, followed by pulmonary and tracheobronchial, was the most vulnerable deposition region, and children were the most susceptible age group. Inhalation risk assessment of TEs revealed significant non-carcinogenic as well as carcinogenic risk, especially for biomass fuel users. The potential years of life lost (PYLL) was the highest for chronic obstructive pulmonary disease (COPD: 15.9 ± 3.8 years) followed by lung cancer (10.3 ± 0.3 years) and pneumonia (10.1 ± 0.1 years), while the PYLL rate was also highest for COPD, with Cr(VI) being the major contributor. Overall, these findings reveal the significant health burden faced by the northeastern Indian population from indoor cooking using solid biomass fuels.

Estimating the Wind Dependency of Aerosol Optical Depth at Remote Oceanic Regions

In this article, the applicability of India’s indigenously developed scatterometer, Scatsat-1 for marine aerosol characterization and wind dependency of aerosol optical depth (AOD) was investigated using 3 years of satellite data. Wind data from Scatsat-1 and AOD with its size fraction from SNPP VIIRS from 2017 to 2019 were used for the investigation. A technique has been demonstrated for identifying remote oceanic regions with mostly marine aerosol using certain criteria like distance from land, higher fraction of coarse AOD, lower variation of AOD with wind direction, and so forth. Daily wind and AOD from 2017 to 2019 were used for studying the relationship between wind speed and AOD at remote oceanic locations away from terrestrial and anthropogenic influence. Five regions of interest (ROIs) of 5° by 5° were identified in different oceanic regions for carrying out the regression analysis. A linear increase of coarse mode AOD and total AOD with an increase in wind speed was observed for all five remote locations while fine mode AOD was unrelated. The slope of the linear relation agreed with Kiliyanpilakkil and Meskhidze (2011) for intermediate wind values. The remote regions also had a lower variation of AOD with change in wind direction implying less transport of aerosol from nearby landmasses.

Exposure to airborne SARS-CoV-2 in four hospital wards and ICUs of Cyprus. A detailed study accounting for day-to-day operations and aerosol generating procedures

In any infectious disease, understanding the modes of transmission is key to selecting effective public health measures. In the case of COVID-19 spread, the strictness of the imposed measures outlined the lack of understanding on how SARS-CoV-2 transmits, particularly via airborne pathways. With the aim to characterize the transmission dynamics of airborne SARS-CoV-2, 165 and 62 air and environmental samples, respectively, were collected in four COVID-19 wards and ICUs in Cyprus and analyzed by RT-PCR. An alternative method for SARS-CoV-2 detection in air that provides comparable results but is less cumbersome and time demanding, is also proposed. Considering that all clinics employed 14 regenerations per hour of full fresh air inside patient rooms, it was hypothesized that the viral levels and the frequency of positive samples would be minimum outside of the rooms. However, it is shown that leaving the door opened in patient rooms hinders the efficiency of the ventilation system applied, allowing the virus to escape. As a result, the highest observed viral levels (135 copies m−3) were observed in the corridor of a ward and the frequency of positive samples in the same area was comparable to that inside a two-bed cohort. SARS-CoV-2 in that corridor was found primarily to lie in the coarse mode, at sizes between 1.8 and 10 μm. Similar to previous studies, the frequency of positive samples and viral levels were the lowest inside intensive care units. However, if a patient with sufficient viral load (Ct-value 31) underwent aerosol generating procedures, positive samples with viral levels below 45 copies m−3 were acquired within a 2 m distance of the patient. Our results suggest that a robust ventilation system can prevent unnecessary exposure to SARS-CoV-2 but with limitations related to foot traffic or the operations taking place at the time.

Molecular Composition, Seasonal Variation, and Size Distribution of n-Alkanes, PAHs, and Saccharides in a Medium-Sized City of Guanzhong Plain, Northwest China: Evaluation of Control Measures Executed in the Past Decade.

Baoji is a medium-sized city in the Guanzhong Plain of northwest China. The compositions of three important organic groups, namely n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and saccharides in atmospheric aerosol with different aerodynamic diameters in power were determined. Both seasonal and daily trends of the target organic chemical groups were demonstrated. The concentration levels of total quantified n-alkanes and saccharides in total suspended particles (TSP) in winter were 541 ± 39 and 651 ± 74 ng·m-3, respectively, much higher than those of the other three seasons. A high total quantified PAHs concentration level of 59.6 ± 6.4 ng·m-3 was also seen in wintertime. n-Alkanes showed a bimodal percent distribution in spring, autumn, and winter. Two peaks were found with the particle sizes of 0.7 μm < Dp < 2.1 μm and 3.3 μm < Dp < 4.7 μm, respectively. In summer, a unimodal was seen with a peak of 4.7 μm < Dp < 5.8 μm. Dehydrated saccharides and PAHs present a unimodal size distribution peaking at the aerodynamic diameters of 0.7 µm < Dp < 2.1 µm. In contrast to glucose and fructose, they mainly exist in the coarse mode particles and have the highest concentrations at aerodynamic diameters of 4.7 µm < Dp < 9.0 µm. The geometric mean diameters (GMD) of n-alkanes and saccharides of the fine particles in winter were higher than in the other seasons. Compared with the data in 2008, the fossil fuel-derived n-alkanes and PAHs in winter decreased by nearly an order of magnitude in 2017. Both the carbon preference index (CPI) of n-alkanes and the diagnostic ratios of PAHs suggest that coal combustion and vehicle exhaust were the major pollution sources of the organic groups in the two decades. It should be noted that the contribution of traffic emissions greatly increased from 2008 to 2017, consistently with a large raise of registered vehicles in Baoji city. The overall results confirm that the control measures conducted by the local government in the recent decade mitigated the air pollution in this city.

Size-Resolved Field Performance of Low-Cost Sensors for Particulate Matter Air Pollution.

Particulate matter (PM) air pollution is a major health hazard. The health effects of PM are closely linked to particle size, which governs its deposition in (and penetration through) the respiratory tract. In recent years, low-cost sensors that report particle concentrations for multiple-sized fractions (PM1.0, PM2.5, PM10) have proliferated in everyday use and scientific research. However, knowledge of how well these sensors perform across the full range of reported particle size fractions is limited. Unfortunately, erroneous particle size data can lead to spurious conclusions about exposure, misguided interventions, and ineffectual policy decisions. We assessed the linearity, bias, and precision of three low-cost sensor models, as a function of PM size fraction, in an urban setting. Contrary to manufacturers' claims, sensors are only accurate for the smallest size fraction (PM1). The PM1.0-2.5 and PM2.5-10 size fractions had large bias, noise, and uncertainty. These results demonstrate that low-cost aerosol sensors (1) cannot discriminate particle size accurately and (2) only report linear and precise measures of aerosol concentration in the accumulation mode size range (i.e., between 0.1 and 1 μm). We recommend that crowdsourced air quality monitoring networks stop reporting coarse (PM2.5-10) mode and PM10 mass concentrations from these sensors.