Single particle analyses of black carbon (BC) particles in precipitation samples are necessary to elucidate the BC climatic impact attributable to natural and anthropogenic combustion activities. For practical reasons, snow and ice core samples are often melted and stored as liquid in vials before analysis. We evaluated storage methods of samples after melting to assess BC measurement accuracy by transmission electron microscopy (TEM) and a Single Particle Soot Photometer (SP2) combined with a nebulizer. TEM analysis of ultrapure water samples stored in borosilicate glass vials revealed that nebulized particles contained significant amounts of silicate and sodium eluted from glass vials. Because such eluted materials interfere with individual particle observations, plastic vials should be used for TEM analysis. In contrast, mass concentrations and size distributions of BC in snow samples measured by SP2 after 6-week storage as liquid in glass and PET (a plastic) vials were comparable to the initial concentrations and distributions, indicating that interference from glass-eluted materials was negligible for BC measurements by SP2. Repeated measurements of ice core samples revealed that BC mass concentrations and size distributions for both vials remained stable in most of the samples over several months, although significant BC losses occurred in some samples stored in PET vials. The mass concentration vastly decreased (28% on average) after storage for refrozen-thawed snow samples, suggesting it is unsuitable for accurate BC measurement. Our results demonstrate the great importance of vial choice for analyzing nebulized particles, depending on the analytical method and sample storage period.Copyright (c) 2025 American Association for Aerosol Research

Over the Northwest Pacific off Hokkaido, low clouds such as stratocumulus, stratus, and fog form frequently in summer. Despite the scientific and socioeconomic importance of these low clouds, our understanding of their reproducibility in weather prediction models under different synoptic circumstances is still lacking. This study assesses the ability of low-cloud representation and prediction in the Japan Meteorological Agency Meso-Scale Model (MSM) mainly in June and July 2020-2022, focusing particularly on synoptic fluctuations of near-surface temperature advection and low-cloud fraction. The low-cloud fraction predicted from the preceding day corresponds quite well with that in the analysis. However, the low-cloud fraction in the analysis is not highly correlated with satellite observations on daily timescales, while the mean low-cloud fraction agrees with the observations. The MSM sometimes simulates unrealistic fog within the near-surface stable layer associated with warm advection, resulting in a positive cloud fraction bias and a negative downward shortwave radiation bias. Under both warm and cold advection, the MSM may also underestimate the low-cloud fraction, although it still reproduces the horizontal distribution of low clouds rather consistently with satellite observations.

Black carbon (BC) is a crucial component among light-absorbing aerosols, significantly impacting Earth's radiation budget. BC in the atmosphere absorbs sunlight and leads to atmospheric heating, while BC deposited on snow and ice surfaces reduces albedo, accelerating snowmelt. Additionally, BC can serve as cloud condensation nuclei and ice nucleating particles. Understanding the historical role of BC in pristine environments, particularly in the Arctic, where climate and environmental changes have been pronounced, is vital. However, data on preindustrial BC levels remain sparse, with limited observations unaffected by anthropogenic sources. Ice cores offer valuable proxy records of BC concentrations and size distributions since the preindustrial era. In this study, we analyzed an ice core retrieved from the EastGRIP site in Northeast Greenland, reaching a depth of 133 meters, using a Continuous Flow Analysis (CFA) system at the National Institute of Polar Research. The CFA system facilitated high-resolution data collection on BC, stable isotopes of water, microparticles, and eight elements (Na, Mg, Al, Si, S, K, Ca, Fe). For BC analysis, we employed a recently developed Wide-range (WR) SP2 (Single Particle Soot Photometer) capable of detecting BC particles in the size range of 70 to 4000 nm. The combination of WR-SP2 and a high-efficiency nebulizer enabled precise measurements of BC concentrations and size distributions. The core was dated through annual layer counting primarily using Na concentrations, supplemented by microparticle and Ca concentrations. As reference horizons, we used volcanic sulfate peaks and tritium peaks from nuclear bomb testing. We present the EastGRIP BC record spanning the past 350 years and compare it with previously obtained BC records from Greenland. Our findings reveal that both the number and mass concentrations of BC at EastGRIP began to increase around 1860, driven by the influx of anthropogenic BC. These concentrations peaked around 1920 and have since declined. While this temporal trend aligns with other Greenland sites, it differs slightly from that observed in southern Greenland, potentially reflecting variations in emission source contributions between northern and southern Greenland. Notably, anthropogenic BC at EastGRIP exhibited larger sizes than biomass-burning BC, consistent with previous findings for the SIGMA-D site in Northwest Greenland. In the preindustrial period, BC concentrations showed their peak during summer. However, the inflow of anthropogenic BC has shifted the peak season from summer to winter/early spring. Unlike SIGMA-D, the BC peak season did not revert to summer in the 1990s. Our accurate, high temporal-resolution data on BC concentrations and sizes offer crucial insights into understanding BC sources, transport pathways, and deposition processes. Furthermore, this new dataset serves to constrain and validate aerosol and climate models, ultimately improving projections for future climate and environmental conditions.

An integrated observational study of aerosols and clouds was carried out in summer 2022 over the western North Pacific (off the eastern coast of Hokkaido, Japan) using both an aircraft and a research vessel for the first time in this area. The aim of this experiment was to characterize the physical and chemical properties of aerosols and to evaluate the contributions of anthropogenic and natural emissions to cloud condensation nuclei (CCN) and ice-nucleating particle (INP) concentrations. The experiment also aims to examine the vertical structure of low-level clouds, which have high radiative effects, over this region. Here, we present an overview of the experiment and some preliminary results. Onboard the research vessel, suspended particulate matter in seawater was sampled, and the size distributions of dominant particle types (e.g., diatom fragments and organic matter) were determined. By analyzing atmospheric aerosols sampled from aircraft, we derived the number size distributions of dust-like particles in the air far from source regions. The aerosol size distributions, as measured from both the vessel and aircraft, suggested that most of the aerosols that could act as CCN were of anthropogenic origin: The upper-bound estimate of the sea spray aerosol (SSA) contribution to the CCN concentration at altitudes below 1200 m was 23

The roles and impacts of refractory black carbon (rBC), an important aerosol species affecting Earth's radiation budget, are not well understood owing to a lack of accurate long-term observations. To study the temporal changes in rBC since the pre-industrial period, we analyzed rBC in an ice core drilled in northwestern Greenland. Using an improved technique for rBC measurement and a continuous flow analysis (CFA) system, we obtained accurate and high-temporal-resolution records of rBC particle size and mass/number concentrations for the past 350 years. Number and mass concentrations, which both started to increase in the 1870s associated with the inflow of anthropogenically derived rBC, reached their maxima in the 1910s–1920s and then subsequently decreased. Backward-trajectory analyses suggest that North America was likely the dominant source region of the anthropogenic rBC in the ice core. The increase in anthropogenic rBC shifted the annual concentration peaks of rBC from summer to winter–early spring. After rBC concentrations diminished to pre-industrial levels, the annual peak concentration of rBC returned to the summer. We found that anthropogenic rBC particles were larger than biomass burning rBC particles. By separating the rBC in winter and summer, we reconstructed the temporal variations in rBC that originated from biomass burning, including the period with large anthropogenic input. The rBC that originated from biomass burning showed no trend in increase until the early 2000s. Finally, possible albedo reductions due to rBC are discussed. Our new data provide key information for validating aerosol and climate models, thereby supporting improved projections of future climate and environment.

Aerosol composition and mixing state influence its ability to form cloud droplets and ice crystals and to scatter and absorb sunlight, all of which affect its impact on climate. In this study, aerosol samples were collected from different altitudes, ranging from the sea surface to similar to 8000 m, over the ocean in the western North Pacific in the summer of 2022 using an aircraft and a research vessel. The samples were classified into three periods based on the sampled air parcel sources: ocean and desert (period 1), Siberian Forest biomass burning event (period 2), and their mixtures (period 3). Measurements of particle composition using transmission electron microscopy with energy-dispersive X-ray spectrometry revealed that samples from period 1 had high sea salt and mineral dust fractions, whereas samples from period 2 had high fractions of potassium-bearing particles with organics and black carbon. Samples from period 3 showed influences of both sea spray and biomass burning. During periods 1 and 3, the sea salt fractions increased as the samples were collected at lower altitudes. The compositions of biomass burning and sea spray were mixed at individual particles, with higher fractions of Na and K during period 1 and period 2, respectively, than in other periods. Our analysis of individual particles revealed a wide range of compositions and mixing states of particles, which depend on the aerosol source, size, and altitude. These factors need to be considered when evaluating aerosol composition and mixing state, both of which affect aerosol climate effects.

Black carbon (BC) aerosol, released into the atmosphere from fuel combustion and biomass burning, is known to be an important short-lived climate forcer (SLCF) because it efficiently absorbs solar radiation and directly heats the atmosphere. Because its accumulation on snow and ice promotes their melting, BC is an important driver of warming, particularly in the Arctic region. Observed surface BC concentrations in the Arctic region show typical seasonal variations, increasing during the winter and spring and decreasing during the warmer season with some peak events in few months of summer, along with large interannual variations. The present study investigates the primary factors influencing the differences in the spatiotemporal surface concentrations of BC in the Arctic region by performing a hemispheric-scale air-quality simulation for the years 2015 and 2016. The model reasonably simulates the observed BC concentration levels and their seasonal patterns, as well as their differences between these two years. This study shows that large year-to-year variability in BC-rich air-mass pathways, such as long-range transport from surrounding regions, and besides these air-mass stagnation within the Arctic region, influence the differences in the Arctic BC concentrations between 2015 and 2016. In addition, the Arctic BC concentrations were also controlled by interannual variations in the amount and distribution of emissions due to the size and the location of open fires, including both Asian crop residue burning in spring and boreal forest fires in summer.

The extensive emissions of black carbon (BC) from the Indo-Gangetic Plain (IGP) region of India have been well recognized. Particularly, biomass emissions from month-specific crop-residue burning (April, May, October, November) and heating activities (December-February) are considered substantial contributors to BC emissions in the IGP. However, their precise contribution to ambient BC aerosol has not been quantified yet and remains an issue of debate. Therefore, this study aims to fill this gap by quantifying the contribution of these month-specific biomass emissions to ambient BC at an urban site in IGP. This study presents the analysis of BC mass concentrations (M-BC) measured for 3 years (2020-2022) in Delhi using an optical photometer i.e., continuous soot monitoring system (COSMOS). A statistical analysis of monthly mean M-BC and factors affecting the M-BC (ventilation coefficients, air mass back trajectories, fire counts) is performed to derive month-wise contribution due to background concentration, conventional emission, regional transport, crop-residue burning, and heating activities. The yearly mean M-BC (5.3 +/- 4.7, 5.6 +/- 5.0, and 5.3 +/- 3.5 mu g m(-3) during 2020, 2021, and 2022, respectively) remained relatively consistent with repetitive monthly patterns in each year. The peak concentrations were observed from November to January and low concentrations from June to September. Anthropogenic activities contributed significantly to M-BC over Delhi with background concentration contributing only 30 % of observed M-BC. The percentage contribution of emissions from crop-residue burning varied from 15 % (May) to 37 % (November), while the contribution from heating activities ranged from 25 % (December) to 39 % (January). This source quantification study highlights the significant impact of month-specific biomass emissions in the IGP and can play a vital role in better management and control of these emissions in the region.

Ice cores can provide long-term records of refractory black carbon (rBC), an important aerosol species closely linked to the climate and environment. However, previous studies of ice cores only analyzed rBC particles with a diameter of < 500 nm, which could have led to an underestimation of rBC mass concentrations. Information on the size distribution of rBC particles is very limited, and there are no Arctic ice core records of the temporal variation in rBC size distribution. In this study, we applied a recently developed improved technique to analyze the rBC concentration in an ice core drilled at the SIGMA-D site in northwestern Greenland. The improved technique, which uses the modified Single-Particle Soot Photometer (SP2) and a high-efficiency nebulizer, widens the measurable range of rBC particle size. For high-resolution continuous analyses of ice cores, we developed a continuous flow analysis (CFA) system. Coupling of the improved rBC measurement technique with the CFA system allows accurate high-resolution measurements of the size distribution and concentration of rBC particles with a diameter between 70 nm and 4 m, with minimal particle losses. Using this technique, we reconstructed the size distributions and the number and mass concentrations of rBC particles during the past 350 years. On the basis of the size distributions, we assessed the underestimation of rBC mass concentrations measured using the conventional SP2s. For the period 2003-2013, the underestimation of the average mass concentration would have been 12 %-31 % for the SIGMA-D core.

To investigate the effects of the regulations of diesel and non-methane hydrocarbon (NMHCs) emissions in the Tokyo metropolitan area (TMA) on the characteristics of carbonaceous aerosols (organic carbon (OC) and elemental carbon (EC)), we conducted field observations to characterize carbonaceous aerosols in the TMA in the summer of 2004 and 2014 (the end of July–middle of August). Following the enforcement of diesel emission regulations, EC concentrations showed a four-fold decrease from 2004 to 2014. However, OC concentrations showed no significant decrease in the last decade. Multiple chemical analyses revealed the differences in the impacts of the contribution of oxygenated fraction, biogenic NMHCs on OC, and the secondary organic aerosol—Ozone relationship between 2004 and 2014. Further investigations into the emission inventory for recent years, especially in terms of precursor gases, are needed for better prediction of OC in the TMA using chemical transport models.

In simulations of Arctic mixed-phase clouds, cloud persistence and the liquid water path (LWP) are sensitive to ice particle number concentrations. Here, we explore sensitivities of cloud microphysical properties to the dominant ice particle shape (dendrites, plates, columns, or spheres) using the SCALE-AMPS large-eddy simulation model. AMPS is a bin microphysics scheme that predicts particle shapes based on the inherent growth ratio (IGR) of spheroids, which determines vapor depositional growth rates along the a and c axes, and the rimed and aggregate mass fractions. We examine the impacts of various IGR values on simulations of clouds observed during the M-PACE and SHEBA experiments. Under M-PACE (SHEBA) conditions, LWP varies between 49 (1.1) and 230 (6.7) g m-2, and the ice water path (IWP) varies between 3 (0.03) and 40 (0.12) g m-2, depending on the ice shape. The lowest LWP and the highest IWP are obtained when columnar particles dominate because their low terminal velocities and large capacitance and collisional area result in large vapor deposition and riming rates, whereas the highest LWP and lowest IWP are obtained when spherical particles dominate because their vapor deposition and riming rates are low. Because ice particle shape significantly influences simulated Arctic mixed-phase clouds, reliable simulations require accurately estimated IGR values under various atmospheric conditions. Finally, comparisons between the simulation results and observations show that the size distribution larger than 2000 mm is better reproduced when the increase in rimed mass that causes ice particles to become spherical is suppressed.

Abstract The roles of Arctic aerosols as ice-nucleating particles remain poorly understood, even though their effects on cloud microphysics are crucial for assessing the climate sensitivity of Arctic mixed-phase clouds and predicting their response to Arctic warming. Here we present a full-year record of ice-nucleating particle concentrations over Svalbard, where surface warming has been anomalously faster than the Arctic average. While the variation of ice-nucleating particles active at around −30 °C was relatively small, those active at higher temperatures (i.e., highly active ice-nucleating particles) tended to increase exponentially with rising surface air temperatures when the surface air temperatures rose above 0 °C and snow/ice-free barren and vegetated areas appeared in Svalbard. The aerosol population relevant to their increase was largely characterized by dust and biological organic materials that likely originated from local/regional terrestrial sources. Our results suggest that highly active ice-nucleating particles could be actively released from Arctic natural sources in response to surface warming.

Long-term measurements of the mass concentration of black carbon (BC) in the atmosphere (MBC) with well-constrained accuracy are indispensable to quantify its emission, transport, and deposition. The aerosol light absorption coefficient (babs), usually measured by a filter-based absorption photometer, including an Aethalometer (AE), is often used to estimate MBC. The measured babs is converted to MBC by assuming a value for the mass absorption cross section (MAC). Previously, we derived the MAC for AE (MAC (AE)) from measured babs and independently measured MBC values at two sites in the Arctic. MBC was measured with a filter-based absorption photometer with a heated inlet (COSMOS). The accuracy of the COSMOS-derived MBC (MBC (COSMOS)) was within about 15%. Here, we obtained additional MAC (AE) measurements to improve understanding of its variability and uncertainty. We measured babs (AE) and MBC (COSMOS) at Alert (2018-2020), Barrow (2012-2022), Ny-angstrom lesund (2012-2019), and Pallas (2019-2022). At Pallas, we also obtained four-wavelength photoacoustic aerosol absorption spectrometer (PAAS-4 lambda) measurements of babs. babs (AE) and MBC (COSMOS) were tightly correlated; the average MAC (AE) at the four sites was 11.4 +/- 1.2 m2 g-1 (mean +/- 1 sigma) at 590 nm and 7.76 +/- 0.73 m2 g-1 at 880 nm. The spatial variability of MAC (AE) was about 11% (1 sigma), and its year-to-year variability was about 18%. We compared MAC (AE) in the Arctic with values at mid-latitudes, measured by previous studies, and with values obtained by using other types of filter-based absorption photometer, and PAAS-4 lambda.Copyright (c) 2024 American Association for Aerosol Research

AbstractOceanic suspended particulate matter (SPM) plays important roles in the coupling of climate and biogeochemical cycles via ocean–atmosphere interactions. However, methods for quantifying the properties of SPM in seawater have not yet been well established. Here we present the application of the recently developed complex amplitude sensor (CAS) for analyzing the complex forward-scattering amplitude of individual SPM (0.2–5.0 µm in diameter) obtained at depths of 0–100 m during a research cruise in the western North Pacific. The measured distribution of the complex amplitude indicated that the CAS-derived SPM data could be roughly classified into five major types. Comparison with reference sample’s complex amplitude data and scanning electron microscopy analysis suggested that these types could be attributed mainly to diatom fragments, carbonaceous materials (likely organic matter), mineral dusts, iron oxides, or black carbon. Depth profiles revealed that relatively high concentrations of SPM, presumably dominated by diatom fragments and carbonaceous materials with peak diameters of 0.7–1.0 µm, were typically associated with elevated turbidities and chlorophyll a concentrations. Based on this case study, we discuss the practical advantages and limitations of using the CAS to measure size-resolved concentrations of SPM in seawater and to characterize its composition.

An objective soft x-ray flat-field spectrograph employing a laminar-type bilayer coated, varied-line-spacing, spherical grating was designed to improve the detection limit and sensitivity of soft x-ray flat-field spectrographs in a region of 250-550 eV. As a design criterion, spectral flux, SF, [Hatano et al., Appl. Opt. 60, 4993-4999 (2021)], which is proportional to the amount of optical flux incident onto a detector and correlated with detection sensitivity, was used to be maximized. To enhance reflectivity with the coating design, Au/Ni bilayer coating was investigated to optimize the incidence angle and thickness of the Ni layer. This is based on the consideration that, in an energy region of over 400 eV, refractive indices of Au (bottom layer), Ni (top layer), and vacuum are increased from the bottom to the top of the layers, and a supplemental enhancement of reflectivity can be expected by optimizing the thickness of the top layer. Thus, the thickness of Ni and the incidence angle were chosen to be 8.0 nm and 86.00 degrees, respectively. To maintain dispersion and spectral resolution of the grating used at an incidence angle of 87.07 degrees as previously designed, groove density was increased to 1500 lines/mm from 1200 lines/mm of our previous design. Finally, a holographic, varied-line-spacing, spherical grating was designed assuming an aspherical-wavefront-recording configuration. The numerical simulation results showed that the spectrograph employing newly designed grating with laminar-type grooves and Au/Ni bilayer coating exhibited 2-18 times higher spectral flux as well as an improved spectral resolution compared with those obtained with the previously designed gratings and spectrographs.

During the PAMARCMiP 2018 campaign (March and April 2018) a proton-transfer-reaction mass spectrometer (PTR-MS) was deployed onboard the POLAR 5 research aircraft and sampled the high Arctic atmosphere under Arctic haze conditions. More than 100 compounds exhibited levels above 1 pmol/mol in at least 25% of the measurements. We used acetone mixing ratios, ozone concentrations, and back trajectories to identify periods with and without long-range transport from continental sources. During two flights, surface ozone depletion events (ODE) were observed that coincided with enhanced levels of acetone, and methylethylketone, and ice nucleating particles (INP).Air masses with continental influence contained elevated levels of compounds associated with aged biogenic emissions and anthropogenic pollution (e.g., methanol, peroxyacetylnitrate (PAN), acetone, acetic acid, meth-ylethylketone (MEK), proprionic acid, and pentanone). Almost half of all positively detected compounds (>100) in the high Arctic atmosphere can be associated with terpene oxidation products, likely produced from mono-terpenes and sesquiterpenes emitted from boreal forests. We speculate that the transport of biogenic terpene emissions may constitute an important control of the High Arctic aerosol burden. The sum concentration of the detected aerosol forming vapours is-12 pmol/mol, which is of the same order than measured dimethylsulfide (DMS) mixing ratios and their mass density corresponds to approximately one fifth of the measured non-black -carbon particles.

The Arctic region is warming about four times faster than the rest of the globe, and thus it is important to understand the processes driving climate change in this region. Aerosols are a significant component of the Arctic climate system as they form ice crystals and liquid droplets that control the dynamics of clouds and also directly interact with solar radiation, depending on the compositions and mixing states of individual particles. Here, we report on the characteristics of submicron-sized aerosol particles using transmission electron microscopy obtained at two high Arctic sites, northeast Greenland (Villum Research Station) and Svalbard (Zeppelin Observatory), during spring 2018. The results showed that a dominant compound in the submicron-sized spring aerosols was sulfate, followed by sea salt particles. Both model simulations and observations at the Zeppelin Observatory showed that sea salt particles became more prevalent when low-pressure systems passed by the station. Model simulations indicate that both sampling sites were affected by diffused and diluted long-range transport of anthropogenic aerosols from lower latitudes with negligible influences of biomass burning emissions during the observation period. Overall, the composition of measured aerosol particles from the two Arctic sites was generally similar and showed no apparent variation except for the sea salt fractions. This study shows a general picture of high Arctic aerosol particles influenced by marine sources and diffused long-range transport of anthropogenic sources during the Arctic spring period. These results will contribute to a better knowledge of the aerosol composition and mixing state during the Arctic spring, which helps to understand the contributions of aerosols to the Arctic climate.

Black carbon (BC) from anthropogenic and natural sources has a pronounced climatic effect on the polar environment. The interaction of BC with low-level Arctic clouds, important for understanding BC deposition from the atmosphere, is studied using the first long-term observational data set of equivalent black carbon (eBC) inside and outside of clouds observed at Zeppelin Observatory, Svalbard. We show that the measured cloud residual eBC concentrations have a clear seasonal cycle with a maximum in early spring, due to the Arctic haze phenomenon, followed by cleaner summer months with very low concentrations. The scavenged fraction of eBC was positively correlated with the cloud water content and showed lower scavenged fractions at low temperatures, which may be due to mixed-phase cloud processes. A trajectory analysis revealed potential sources of eBC and the need to ensure that aerosol-cloud measurements are collocated, given the differences in air mass origin of cloudy and non-cloudy periods.

Considering the significance of PM1 aerosol in assessing health impacts of air pollution, an extensive analysis of PM1 samples collected at an urban site in Delhi is presented in this study. Overall, PM1 contributed to about 50 % of PM2.5 mass which is alarming especially in Delhi where particle mass loadings are usually higher than prescribed limits. Major portion of PM1 consisted of organic matter (OM) that formed nearly 47 % of PM1 mass. Elemental carbon (EC) contributed to about 13 % of PM1 mass, whereas SO42- (16 %), NH4+ (10 %), NO3-(4 %) and Cl-(3 %) were the major inorganic ions present. Sampling was performed in two distinctive campaign periods (in terms of meteoro-logical conditions and heating (fire) activities), during the year 2019, each spanning two-week time, i.e. (i) September 3rd-16th (clean days), and (ii) November 22nd-December 5th (polluted days). Additionally, PM2.5 and black carbon (BC) were measured simultaneously for subsequent analysis. The 24-h averaged mean concentrations of PM2.5 and BC dur-ing clean days (polluted days) were 70.6 & PLUSMN; 26.9 and 3.9 & PLUSMN; 1.0 & mu;g m-3 (196 & PLUSMN; 104 and 7.6 & PLUSMN; 4.1 & mu;g m-3), respectively, which were systematically lower (higher) than that of the annual mean (taken from studies conducted at same site in 2019) of 142 and 5.7 & mu;g m-3, respectively. Changes in characteristic ratios (i.e., organic carbon (OC)/el- emental carbon (EC) and K+/EC) of chemical species detected in PM1 show an increase in biomass emissions during polluted days. Increase in biomass emission can be attributed to increase in heating practices (burning of biofuels such as wood logs, straw, and cow-dung cake) in- and around- Delhi because of fall in temperature during second campaign. Furthermore, a significant increase in NO3- fraction of PM1 is observed during second campaign which shows fog pro- cessing of NOX due to conducive meteorological conditions in winters. Also, comparatively stronger correlation of NO3- with K+ during second campaign (r = 0.98 as compared to r = 0.5 during first campaign) suggests the increased heating practices to be a contributing factor for increased fraction of NO3- in PM1. We observed that during polluted days, meteorological parameters such as dispersion rate also played a major role in intensifying the impact of increased local emissions due to heating activities. Apart from this, change in the direction of regional emission transport to study site and the topology of Delhi are the possible reasons for the elevated pollution level, especially PM1 during winter in Delhi. This study also suggests that black carbon measurement techniques used in current study (optical absorbance with heated inlet and evolved carbon techniques) can be used as reference techniques to determine the site-specific calibration constant of optical photometers for urban aerosol.

Laminar-type spherical diffraction gratings overcoated with carbon-based materials were designed, fabricated, and evaluated for the purpose of enhancing the analytical sensitivity of the flat-field spectrograph in a vacuum ultraviolet region of 35–110 eV. As the design benchmark for numerical calculations, diffraction efficiency (DE) and spectral flux, which are defined by the product of the DE and numerical aperture and correlate with the analytical sensitivity of the spectrograph, were used. To simplify the feasibility study on the overcoating effects, we assumed a laminar-type grating having a grating constant of 1/1000 mm and coated with a Au layer of 30.0 nm thickness and an incidence angle of 84.0°. The optimized groove depth and duty ratio were 30.0 nm and 0.3, respectively. In addition, the optimum thicknesses of the overcoating layer were 44, 46, 24, and 30 nm for B4C, C, diamond-like-carbon, and SiC, respectively. Based on these results, we have fabricated a varied-line-spacing holographic grating overcoated with B4C with a thickness of 47 nm. For the experimental evaluation, we used the light source of Mg-L and Al-L emissions excited by the electron beam generated from an electron microscope, an objective flat-field spectrograph, and a CCD imaging detector. The experimental results showed that the spectrograph employing a new grating overcoated with the B4C layer indicated almost the same spectral resolution and 2.9–4.2 times higher analytical sensitivity compared with those obtained with a previously designed Au-coated grating having a grating constant of 1/1200 mm and used at an incidence of 86.0°.