Coarse Mode Particles Research Articles

Aerosol type classification and its temporal distribution in Kanpur using ground-based remote sensing

Based on AERONET version 3 level 2 inversion products, we classify aerosol types and investigate their temporal distribution in the atmosphere using particle linear depolarization ratio (PLDR) and single scattering albedo (SSA) at the wavelength of 1020 nm over Kanpur. It is for the first time over the North Indian region the work has been emphasized. The remarkable findings over Kanpur station indicate that SSA and coarse-mode particles in the atmosphere increased with increasing PLDR at 440, 675, 870, and 1020 nm wavelengths. It is observed in the 2-dimensional histogram that the rate of occurrence of aerosols is high when the fine mode fraction (FMF) is high and the dust ratio (Rd) is low. The atmosphere of Kanpur is partially influenced by dust-dominated mixture (DDM), pollution-dominated mixture (PDM), and pure dust (PD) with 53% whereas, the rest of the dust-free pollution aerosols are 47%. The annual mean occurrence rate for different aerosol types is 5% for Strongly Absorbing (SA), 20% for Moderately Absorbing (MA), 19% for Weakly Absorbing (WA), 3% for Non-Absorbing (NA), 27% for DDM, 22% for PDM, and 4% for PD, ranging from January 2001 to January 2022. There is a variation in the distribution of various types of pollution particles, which is influenced by the changing seasons. The rate of occurrence of dust-free pollution aerosols is 47%, mostly observed throughout the post-monsoon and winter seasons. The PLDR values in the atmosphere of Kanpur are almost balanced equally because it is affected by both (dust and dust-free) pollution aerosols and the changes can be seen due to the frequent occurrence of dust storms and anthropogenic activities.

Size-resolved molecular characterization of water-soluble organic matter in atmospheric particulate matter from northern China

Atmospheric particulate matter (PM) affects visibility, climate, biogeochemical cycles and human health. Water-soluble organic matter (WSOM) is an important component of PM. In this study, PM samples with size-resolved measurements at aerodynamic cut-point diameters (Dp) of 0.01–18 μm were collected in the rural area of Baoding and the urban area of Dalian, Northern China. Non-targeted analysis was adopted for the characterization of the molecule constitutes of WSOM in different sized particles using Fourier transform-ion cyclotron resonance mass spectrometry. Regardless of the location, the composition of WSOM in Aitken mode particles (aerodynamic diameter <0.05 μm) was similar. The WSOM in accumulation mode particles (0.05–2 μm) in Baoding was predominantly composed of CHO compounds (84.9%), which were mainly recognized as lignins and lipids species. However, S-containing compounds (64.2%), especially protein and carbohydrates species, accounted for most of the WSOM in the accumulation mode particles in Dalian. The CHO compounds (67.6%–79.7%) contributed the most to the WSOM in coarse mode particles (>2 μm) from both sites. Potential sources analysis indicated the WSOM in Baoding were mainly derived from biomass burning and oxidation reactions, while the WSOM in Dalian arose from coal combustion, oxidation reactions, and regional transport.

Regional Aerosol Optical Depth over Antarctica

Atmospheric aerosols greatly contribute to the uncertainty in current climate models, particularly presenting pronounced limitations in the Antarctic region. This study measures aerosol properties using data from several Antarctic AERONET sites (Escudero, Marambio, South Pole, Utsteinen, Vechernaya_Hill) and Zhongshan Station. We examined the spatial and temporal patterns of two specific aerosol properties: Aerosol Optical Depth (AOD) at 500 nm (τ500nm) and Ångström Exponent (AE) between 440 and 870 nm (α440−870nm). Our findings reveal τ500nm medians ranging from 0.02 to 0.09, with elevated values observed along the coastal regions compared to the interior of Antarctica. Regarding the AE, the medians of α440−870nm indicate that the coarse-mode particle aerosols are dominated at Escudero (approximately 0.54). In contrast, fine mode particles prevail at the other sites (over 0.97). Monthly mean τ500nm and the proportion of fine mode particles peaks during austral summer and autumn, suggesting increased marine biological sources. Moreover, analyzing the air mass back trajectories, we discovered marine air influences on Escudero, Marambio, Zhongshan, and Vechernaya_Hill, while Utsteinen and South Pole are primarily experiencing air originating from the Antarctic continent. These findings underscore the significant role of aerosol sources in regional AOD differences. Additionally, higher τ500nm were more associated with significantly negative direct aerosol radiative forcing at the bottom of the atmosphere (DARF-BOA). The direct aerosol radiative forcing at the top of the atmosphere (DARF-TOA) closely correlates with single-scattering albedo (SSA), where high (low) SSA generally results in negative (positive) forcing over Antarctica.

Importance of microphysical settings for climate forcing by stratospheric SO2 injections as modeled by SOCOL-AERv2

Abstract. Solar radiation modification by a sustained deliberate source of SO2 into the stratosphere (strat-SRM) has been proposed as an option for climate intervention. Global interactive aerosol–chemistry–climate models are often used to investigate the potential cooling efficiencies and associated side effects of hypothesized strat-SRM scenarios. A recent model intercomparison study for composition–climate models with interactive stratospheric aerosol suggests that the modeled climate response to a particular assumed injection strategy depends on the type of aerosol microphysical scheme used (e.g., modal or sectional representation) alongside host model resolution and transport. Compared to short-duration volcanic SO2 emissions, the continuous SO2 injections in strat-SRM scenarios may pose a greater challenge to the numerical implementation of microphysical processes such as nucleation, condensation, and coagulation. This study explores how changing the time steps and sequencing of microphysical processes in the sectional aerosol–chemistry–climate model SOCOL-AERv2 (40 mass bins) affects model-predicted climate and ozone layer impacts considering strat-SRM by SO2 injections of 5 and 25 Tg(S) yr−1 at 20 km altitude between 30° S and 30° N. The model experiments consider the year 2040 to be the boundary conditions for ozone-depleting substances and greenhouse gases (GHGs). We focus on the length of the microphysical time step and the call sequence of nucleation and condensation, the two competing sink processes for gaseous H2SO4. Under stratospheric background conditions, we find no effect of the microphysical setup on the simulated aerosol properties. However, at the high sulfur loadings reached in the scenarios injecting 25 Tg(S) yr−1 of SO2 with a default microphysical time step of 6 min, changing the call sequence from the default “condensation first” to “nucleation first” leads to a massive increase in the number densities of particles in the nucleation mode (R&lt;0.01 µm) and a small decrease in coarse-mode particles (R&gt;1 µm). As expected, the influence of the call sequence becomes negligible when the microphysical time step is reduced to a few seconds, with the model solutions converging to a size distribution with a pronounced nucleation mode. While the main features and spatial patterns of climate forcing by SO2 injections are not strongly affected by the microphysical configuration, the absolute numbers vary considerably. For the extreme injection with 25 Tg(S) yr−1, the simulated net global radiative forcing ranges from −2.3 to −5.3 W m−2, depending on the microphysical configuration. Nucleation first shifts the size distribution towards radii better suited for solar scattering (0.3 µm &lt;R&lt; 0.4 µm), enhancing the intervention efficiency. The size distribution shift, however, generates more ultrafine aerosol particles, increasing the surface area density and resulting in 10 DU (Dobson units) less ozone (about 3 % of the total column) in the northern mid-latitudes and 20 DU less ozone (6 %) over the polar caps compared to the condensation first approach. Our results suggest that a reasonably short microphysical time step of 2 min or less must be applied to accurately capture the magnitude of the H2SO4 supersaturation resulting from SO2 injection scenarios or volcanic eruptions. Taken together, these results underscore how structural aspects of model representation of aerosol microphysical processes become important under conditions of elevated stratospheric sulfur in determining atmospheric chemistry and climate impacts.

Characteristics and optical properties of atmospheric aerosols based on long-term AERONET investigations in an urban environment of Pakistan

Radiative balance, local climate, and human health are all significantly influenced by aerosol. Recent severe air pollution over Lahore, a city in Pakistan calls for more thorough research to determine the negative impacts brought on by too many aerosols. To study regional aerosol characteristics and their differences from various aspects, in-depth and long-term (2007–2020) investigations of the columnar aerosol properties over the urban environment of Lahore were carried out by using AERONET data. The Aerosol Optical Depth (AOD400) and Angstrom Exponent (AE400–870) vary from low values of 0.10 to a maximum value of 4.51 and from 0.03 to 1.81, respectively. The huge differences in the amount of AOD440 as well as AE440–870 show the large fluctuation of aerosol classes because of various sources of their emission. During the autumn and winter seasons, the decreasing trend of the optical parameters of aerosols like Single Scattering Albedo (SSA) and Asymmetry Parameter (ASY) with increasing wavelength from 675 to 1020 nm indicates the dominance of light-absorbing aerosols (biomass burning (BB) and industrial/urban (UI). Due to the long-distance dust movement during spring, summer, and autumn, coarse mode particles predominated in Lahore during the study period. Dust type (DD) aerosols are found to be the dominant one during spring (46.92%), summer (54.31%), and autumn (57.46%) while urban industry (BB/UI) was dominant during the winter season (53.21%). During each season, the clean continental (CC) aerosols are found to be in negligible amounts, indicating terrible air quality in Lahore City. The present research work fills up the study gap in the optical properties of aerosols in Lahore and will help us understand more fully how local aerosol fluctuation affects regional climate change over the urban environment of Lahore.

Uncovering the dynamics of atmospheric aerosols in China: A comprehensive analysis of OMI-Retrieved aerosol index data

China faces severe atmospheric problems due to the rapid increase in population and industrialization. Therefore, due to the insufficient number of monitoring stations in such a vast country, remote sensing of an ultraviolet aerosol index (UVAI) provides useful information about absorbing aerosols. This study used the OMI-retrieved UVAI data to investigate the spatial patterns, trends, and periodic nature of UVAI over China from October 2004 to December 2022. Additionally, the correlation and degree of coherence of UVAI with meteorological parameters (temperature & precipitation) and anthropogenic factors (Construction, population, CO2 emission, energy consumption, and primary industry) are also examined. Mean UVAI concentration with an increasing trend of 4.34% per year shows high UVAI values (0.70–1.41) in Xinjiang Uygar followed by Heilongjiang, Jilin, Liaoning, Shandong, Beijing, Hubei, and some northern regions i.e., Gansu, Qinghai, and western Nel Mongol. Seasonally, Xinjiang Uygur experiences high UVAI (<1.52) values during all four seasons with the dominance of both fine and coarse mode particles. Moreover, Hubei, Gansu, Jilin, Shandong, and Xinjiang Uygar experiences high UVAI values i.e. 2.55, 2.05, 1.87, 2.82, 2.27 during 2021 with an increasing trend of 5.50% year−1, 5.43% year−1, 3.82% year−1, 4.73% year−1, and 9.33% year−1 respectively. The HYSPLIT backward trajectories plotted at altitudes of 50m, 100m, and 500m indicate the dominance of desert dust over Jinan, Urumqi, and Lanzhou while anthropogenic pollutants over Wuhan and Changchun. Wavelet coherence (WTC) shows the positive correlation of UVAI with temperature and precipitation. Moreover, the co-variability of absorbing aerosols with anthropogenic and natural factors is also inculcated in this study. Considering the outcomes of this study it will help policymakers to analyze the variability of absorbing aerosols in China and different methods like plantation of more trees, efficient fuel consumption, and promotion of public transport, etc., can be used to reduce air pollution.

Fine Particle Formation and Dependence of Wet Deposition on Precipitation Intensity in an Urban Area

ABSTRACT In order to understand the characteristics of the change of aerosol concentration in an urban area and the impact of meteorological conditions on aerosol concentration in urban areas, particle concentration and size distribution were measured using an aerosol particle counter and an aerosol spectrometer in Hefei, China in spring 2017. Meteorological data, such as temperature, relative humidity, wind speed, wind direction, and shortwave radiation, were measured on a meteorological tower. The concentration of coarse mode (d > 2.5 μm, d is particle diameter), accumulation mode (0.25 μm<d < 2.5 μm), and ultrafine (Aitken and nucleation mode, d < 0.25 μm) particles under different meteorological conditions were recorded. Results show that, approximately 10–20 min after the solar downward shortwave radiation decreases (rises), the ultrafine particles (UFPs) concentration decreases (rises). Diurnal change in radiation causes daily change in the concentration of UFPs, and when the relative humidity was low, UFP generation easily occurs. On wet deposition, the concentration of coarse mode particles is significantly reduced during precipitation, and the concentration of accumulation mode particles varies during heavy precipitation and slight precipitation. Because of the combined action of wet deposition and hygroscopic growth, the concentration of accumulation mode particles first increases and then decreases. And during the slight precipitation, the concentration only increases with the relative humidity.

HETEAC-Flex: an optimal estimation method for aerosol typing based on lidar-derived intensive optical properties

Abstract. This study introduces a novel methodology for the characterization of atmospheric aerosol based on lidar-derived intensive optical properties. The proposed aerosol-typing scheme is based on the optimal estimation method (OEM) and allows the identification of up to four different aerosol components of an aerosol mixture, as well as the quantification of their contribution to the aerosol mixture in terms of relative volume. The four aerosol components considered in this typing scheme are associated with the most commonly observed aerosol particles in nature and are assumed to be physically separated from each other and, therefore, can create external mixtures. Two components represent absorbing and less-absorbing fine-mode particles, and the other two components represent spherical and non-spherical coarse-mode particles. These components reflect adequately the most frequently observed aerosol types in the atmosphere: combustion- and pollution-related aerosol, sea salt, and desert dust, respectively. In addition, to consolidate the calibration and validation efforts for the upcoming EarthCARE mission, the typing scheme proposed here is in accordance with the Hybrid End-To-End Aerosol Classification (HETEAC) model of EarthCARE. The lidar-derived optical parameters used in this typing scheme are the lidar ratio and the particle linear depolarization ratio at two distinct wavelengths (355 and 532 nm), the backscatter-related color ratio for the wavelength pair of 532/1064 nm and the extinction-related Ångström exponent for the wavelength pair of 355/532 nm. These intensive optical properties can be combined in different ways, making the methodology flexible, thus allowing its application to lidar systems with different configurations (e.g., single wavelength or multiwavelength, Raman, high spectral resolution). The typing scheme was therefore named HETEAC-Flex due to its compatibility with EarthCARE's HETEAC and its methodological flexibility. The functionality of the typing scheme is demonstrated by its application to three case studies based on layer-averaged optical properties.

Wind-driven emissions of coarse-mode particles in an urban environment

Abstract. Quantifying surface–atmosphere exchange rates of particles is important for understanding the role of suspended particulate matter in radiative transfer, clouds, precipitation, and climate change. Emissions of coarse-mode particles with a diameter greater than 0.5 µm provide giant cloud condensation nuclei and ice nuclei. These emissions are critical for understanding the evolution of cloud microphysical properties yet remain poorly understood. Here we introduce a new method that uses lidar retrievals of the elastic backscatter and Doppler velocity to obtain surface number emissions of particles with a diameter greater than 0.53 µm. The technique is applied to study particle number fluxes over a 2-month period from 1 June to 10 August 2022 during the TRACER campaign at an urban site near Houston, TX, USA. We found that all the observed fluxes were positive (upwards), indicating particle emission from the surface. The fluxes followed a diurnal pattern and peaked near noon local time. Flux intensity varied through the 2 months with multi-day periods of strong fluxes and multi-day periods of weak fluxes. Emission particle number fluxes peaked near ∼ 100 cm−2 s−1. The daily averaged emission fluxes correlated with friction velocity and were anticorrelated with surface relative humidity. The emission flux can be parameterized as F= 3000 u*4, where u* is the friction velocity in m s−1 and the emission flux F is in cm−2 s−1. The u* dependence is consistent with emission from wind-driven erosion. Estimated values for the mass flux are in the lower range of literature values from non-urban sites. These results demonstrate that urban environments may play an important role in supplying coarse-mode particles to the boundary layer. We anticipate that quantification of these emissions will help constrain aerosol–cloud interaction models that use prognostic aerosol schemes.

Particle Number Size Distribution in Three Different Microenvironments of London

We estimated the particle number distributions (PNDs), particle number concentrations (PNCs), physicochemical characteristics, meteorological effects, and respiratory deposition doses (RDD) in the human respiratory tract for three different particle modes: nucleation (N6–30), accumulation (N30–300), and coarse (N300–10,000) modes. This study was conducted in three different microenvironments (MEs) in London (indoor, IN; traffic intersection, TI; park, PK) measuring particles in the range of 6 nm–10,000 nm using an electrical low-pressure impactor (ELPI+). Mean PNCs were 1.68 ± 1.03 × 104 #cm−3, 7.00 ± 18.96 × 104 #cm−3, and 0.76 ± 0.95 × 104 #cm−3 at IN, TI, and PK, respectively. The PNDs were high for nucleation-mode particles at the TI site, especially during peak traffic hours. Wind speeds ranging from 0 to 6 ms−1 exhibit higher PNCs for nucleation- and accumulation-mode particles at TI and PK sites. Physicochemical characterisation shows trace metals, including Fe, O, and inorganic elements, that were embedded in a matrix of organic material in some samples. Alveolar RDD was higher for the nucleation and accumulation modes than the coarse-mode particles. The chemical signatures from the physicochemical characterisation indicate the varied sources at different MEs. These findings enhance our understanding of the different particle profiles at each ME and should help devise ways of reducing personal exposure at each ME.

Size Distribution and Secondary Formation of Particulate Organic Nitrates in Winter in a Coastal Area

Understanding the size distribution, variation patterns, and potential formation mechanisms of particulate organic nitrates (PONs) is crucial for assessing their influences on atmospheric chemistry, air quality, and the regional climate. This study investigates PONs in the coastal atmosphere of Qingdao, China by collecting size-resolved particulate matter samples and analyzing six types of organic nitrates, namely pinene keto nitrate (PKN229), monoterpene hydroxyl nitrate (MHN215), monoterpene dicarbonyl nitrate (MDCN247), oleic acid hydroxyl nitrate (OAHN361), oleic acid keto nitrate (OAKN359), and pinene sulfate organic nitrate (PSON295), using ultrahigh-performance liquid chromatography(mass spectrometry). The mean total concentration of organic nitrates in fine particles reaches 677 ng m−3. The predominant compound is MHN215, followed by PKN229 and MDCN247. All six organic nitrates exhibited distinct concentration peaks in the droplet mode, with MDCN247 and OAHN361 showing a minor peak in the condensation mode. In addition, an apparent concentration peak is observed in the coarse mode for OAKN359. Comparative analyses under various conditions highlight the significant influences of primary emissions and secondary formation processes on the abundance and size distribution of organic nitrates. For instance, both firework displays during festivals and high NOx emissions from fuel combustion significantly increase the concentrations of condensation-mode organic nitrates, whereas dust particles enhanced the heterogeneous formation of coarse-mode particles. Furthermore, the high humidity of the coastal area promotes aqueous formation in droplet-mode particles.

An analysis of air pollution associated with the 2023 sand and dust storms over China: Aerosol properties and PM10 variability

Every spring, a large part of China is confronted with sand and dust storms (SDS) – mainly originating in the Gobi (including Chinese and Mongolian Gobi) and Taklamakan deserts. In March-April 2023, most of northern, northwestern and northeastern China was struck by three sandstorms that affected an area with more than 500 million people. In this study, aerosol optical, microphysical and radiative properties were studied during these SDS events using an integrated approach that combines satellite, terrestrial and re-analysis data. The results showed that dusty conditions were observed in most areas north of the Yangtze River (Chang Jiang) with daily average PM10 concentrations exceeding 1000 µg/m3 in many cities. VIIRS aerosol optical depth (AOD) at 550 nm during three SDS events exceeded a value of 1 throughout nearly the entire northern part of the country. The AERONET data obtained from the AOE_Baotou site showed a significant increase in total AOD and a corresponding decrease in AE during the SDS. The single scattering albedo (SSA), asymmetry parameter (ASY), real refractive index (RRI) and imaginary refractive index (IRI) values indicate an abundance of scattering coarse-mode particles. Aerosol radiative forcing (ARF) at top of the atmosphere and at the earth's surface was nearly always negative during the period and ranged from −48.5 to +2.7 Wm−2 and from −180.8 to −66.6 Wm−2, resulting in high positive ARF values at ATM (from +63.8 to +132.3 Wm−2). Each of these affects the heating of the atmosphere and cooling on the earth's surface. The atmospheric heating rates ranged from 1.8 to 3.7 K day−1. The formation of these SDS mainly resulted from the passage of cold fronts associated with low pressure systems in the Gobi and Taklamakan deserts, creating conditions for dust to rise into the atmosphere and move further downwind.

Roles of tropical cyclones with varying intensities in the re-distribution of aerosols

The study analyzes three tropical cyclones (TC) with varying intensities, namely BOB02, a deep depression in the Bay of Bengal; Tauktae, an extremely severe cyclone in the Arabian Sea (AS); and Amphan, a supercyclone in the Bay of Bengal, which developed on October 11, 2020, May 13, 2021, and May 16, 2020, respectively. The analysis focuses on studying the re-distribution of the aerosols over the Indian region using these distinct datasets: Modern-Era Retrospective Analysis for Research and Application, version 2 (MERRA2), Integrated Multi-Satellite Retrievals for GPM (IMERG), and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). Throughout the cyclonic period, which includes the period from the inception of the low-pressure area to its dissipation as well as the pre-cyclonic and post-cyclonic periods (one week prior to and after the cyclonic period, respectively), various parameters related to aerosols and background meteorological conditions were collected. The primary parameter of interest was the aerosol optical depth (AOD). The analysis revealed significant variations in meteorological parameters such as wind speed, temperature, relative humidity, and rainfall along the cyclone track during both the cyclonic and post-cyclonic conditions compared to the pre-cyclonic conditions of these TCs. The AOD surrounding the cyclone track decreases during cyclonic and post-cyclonic conditions compared to pre-cyclonic conditions. This is due to the scavenging of both anthropogenic and natural (dust) aerosols. Conversely, AOD increases along the cyclone track, mainly due to an increase in natural (sea salt) aerosols. During pre-cyclonic conditions, both natural (dust) and anthropogenic (black carbon, organic carbon, and sulfate) aerosols contribute significantly to the total AOD, whereas during pre-cyclonic conditions, the main contributors are natural (sea-salt) aerosols. The coarse-mode particles are more dominant during cyclonic and post-cyclonic conditions than pre-cyclonic ones. Furthermore, our observations indicate that the atmospheric boundary layer (ABL) height increases by ∼0.1–0.6 km along the cyclone track during cyclonic conditions compared to pre-cyclonic conditions. While AOD from the free troposphere (FT) contributes more to the total AOD, contributions from ABL increase, while those from the FT decrease during cyclonic and post-cyclonic conditions.

Aerosol-CCN characteristics and dynamics associated with a pre-monsoon dust storm over a high-altitude site in Western Ghats, India.

Aerosol-CCN characteristics and dynamics during a pre-monsoon dust storm (April 6-11, 2015) over a high-altitude site ((17.92°N, 73.66°E, and 1348m above mean sea level (MSL)) in Western Ghats, India, has been studied using ground-based observations, satellite, and reanalysis datasets. Spatial distribution of dust surface mass concentration along with the back trajectory analysis showed the Arabian Desert area (Rub-Al-khali desert) as the source region and strong westerly winds transported the dust particles toward the Indian subcontinent. High values noticed in the surface PM10 (PM2.5), i.e., ~ 450 (~ 130) µg m-3, MODIS AOD550nm (0.6), and MERRA 2 dust surface mass concentration (5 × 10-7kgm-3) along MODIS true color images confirmed the dust storm event on April 6, 2015 over the observational site. Size-segregated aerosol number concentration measured from ground-based observations showed the dominance of Aitken, accumulation, and coarse mode particles during dust period. CCN concentrations at 0.1, 0.3, 0.5, 0.7, and 0.9% SS were analyzed. A low value of CCN concentration and activation fraction (~ 0.3) near surface was noticed during dust storm day, suggesting insoluble mineral dust particle being transported. Analyzed vertical velocity during pre-dust period showed downdraft between 900 and 750hPa, suggesting dust transport from upper altitudes toward the observational site. WRF-Chem model simulation also captured the dust storm event, and the results are in good agreement with the observation with a significance of 95% confidence level.

Physicochemical characterization and source apportionment of Arctic ice-nucleating particles observed in Ny-Ålesund in autumn 2019

Abstract. Ice-nucleating particles (INPs) initiate primary ice formation in Arctic mixed-phase clouds (MPCs), altering cloud radiative properties and modulating precipitation. For atmospheric INPs, the complexity of their spatiotemporal variations, heterogeneous sources, and evolution via intricate atmospheric interactions challenge the understanding of their impact on microphysical processes in Arctic MPCs and induce an uncertain representation in climate models. In this work, we performed a comprehensive analysis of atmospheric aerosols at the Arctic coastal site in Ny-Ålesund (Svalbard, Norway) from October to November 2019, including their ice nucleation ability, physicochemical properties, and potential sources. Overall, INP concentrations (NINP) during the observation season were approximately up to 3 orders of magnitude lower compared to the global average, with several samples showing degradation of NINP after heat treatment, implying the presence of proteinaceous INPs. Particle fluorescence was substantially associated with INP concentrations at warmer ice nucleation temperatures, indicating that in the far-reaching Arctic, aerosols of biogenic origin throughout the snow- and ice-free season may serve as important INP sources. In addition, case studies revealed the links between elevated NINP and heat lability, fluorescence, high wind speeds originating from the ocean, augmented concentration of coarse-mode particles, and abundant organics. Backward trajectory analysis demonstrated a potential connection between high-latitude dust sources and high INP concentrations, while prolonged air mass history over the ice pack was identified for most scant INP cases. The combination of the above analyses demonstrates that the abundance, physicochemical properties, and potential sources of INPs in the Arctic are highly variable despite its remote location.

Long-term observation of columnar aerosol optical properties over the remote South China Sea

The South China Sea (SCS) is a receptor of pollution sources from various parts of Asia and is heavily impacted by strong meteorological systems, which thus dictate aerosol variability over the region. This study analyzes long-term aerosol optical properties observed at Dongsha Island (a representative site in northern SCS) from 2009 to 2021 and Taiping Island (a representative site in southern SCS) from 2012 to 2021 to better apprehend the temporal evolution of columnar aerosols over the SCS. The noticeable difference in loadings, optical properties, and compositions of aerosols between northern and southern SCS was due to the influence of dissimilar emission sources and transport mechanisms. Column-integrated aerosol optical depth (AOD) over northern SCS (range of monthly mean at 500 nm; 0.12–0.51) was significantly greater than southern SCS (0.09–0.21). The maximum AOD in March (0.51 ± 0.28) at Dongsha was attributed to westerlies coupled with biomass-burning (BB) emissions from peninsular Southeast Asia, whereas the maximum AOD at Taiping in September (0.21 ± 0.25) was owing to various pollution from the Philippines, Malaysia, and Indonesia. Fine-mode aerosol dominated over northern SCS (range of monthly mean Angstrom exponent for 440–870 nm: 0.85–1.36) due to substantial influence from continental sources including anthropogenic and BB emissions while coarse-mode particles dominated over southern SCS (0.54–1.28) due to relatively more influence from marine source. More absorbing columnar aerosols prevailed over northern SCS (range of monthly mean single scattering albedo at 675 nm: 0.92–0.99) compared to southern SCS (0.95–0.98) owing to differences in aerosol composition with respect to sources. Special pollution events showcased possible significant impacts on marine ecosystems and regional climate. This study encourages the establishment of more ground-based aerosol monitoring networks and the inclusion of modeling simulations to comprehend the complex nature of aerosol over this vast marginal sea.

Spatial variability and health assessment of particle number concentration at different exposure locations near urban traffic arterial: A case study in Xi'an, China

Urban traffic arteries are considered as hot-spots of pollution of particle number concentration (PNC), but the knowledge of spatial variability and exposure levels of PNC with different particle sizes emitted by vehicles is yet less reported. In this paper, PNC in the size range from 6 to 10,000 nm were measured using the Electrical Low-Pressure Impactor Plus (ELPI+) at four sites near high-density traffic in Xi'an, including one traffic, one roadside, and two urban background. The results showed that PNC was highest at the distance closest to the traffic sources, and decreased exponentially with distance. Vehicle exhaust was the primary source of ambient ultrafine particle (UFP), contributing 60.03% and 54.48% of the number concentration of UFP in the clean and haze weathers, respectively. The average PNCs measured at the traffic site were 2.24 and 3.17 times greater than those at the roadside and urban background sites, respectively. Coarse mode particle concentrations exhibited a higher level at the roadside site due to the secondary dust generated by vehicles. An interesting phenomenon that an inverted U-shaped relationship between measured UFP levels and traffic flows was found when the flow was higher than 6000 veh h−1. Strong spatial inhomogeneity for UFP along the urban road, whereas particles larger than 100 nm in diameter tend to similar concentration distributions. The mean respiratory deposition dose (RDD) at four locations was (7.14 ± 1.12) × 105 particles h−1, with the highest (14.61 ± 2.29) × 1010 particles h−1 at the traffic site. Retired people had a higher exposure of UFP compared to children and adults. This improved understanding of the impact of vehicle emissions on the distribution of PNC near-road.

Application of Gaussian Mixture Models for aerosol type analysis in China

The relative contributions of different aerosol types to the total aerosol content were determined using sun photometer derived inversion data from four Aerosol Robotic Network (AERONET) stations in China, i.e. Beijing, NUIST, Hong Kong PolyU and SACOL. Five main aerosol types were considered: dust (DU), mixed (MI), urban industry (UI), biomass burning (BB) and maritime (MA). The identification of these aerosol types is based on cluster analysis using Gaussian mixture models (GMMs), together with the Mahalanobis distance (MD) to each reference centroid. The results show that the aerosol types are distinctly different between the different sites as regards fine and coarse particles. MI is the dominant aerosol type at four locations, with the largest contribution at NUIST (73.4%). The largest contribution of DU (18.8%) is observed at SACOL and at Beijing the contribution of UI is largest (33.7%). BB contributions are relatively small, with the largest at NUIST (2.7%). For the analysis, two periods are considered, i.e. before and after the implementation of the national ambient air quality standard (GB3095–2012) in 2012. The clustering results revealed a changing trend in the proportion of UI and MI aerosols in Chinese cities. Although the proportion of UI aerosols has increased, MI aerosols still remain dominant. The proportion of DU in SACOL station also increased. The seasonal analysis shows that DU dominates in spring at the SACOL station (55.3%), which is near the dust source area. Among the other stations, the contribution of DU due to long-range transport from the source regions, is largest (10.6%) in Beijing, with a small contribution at NUIST. The aerosol volume size distributions in different regions exhibit substantial differences due to variations in aerosol types: Beijing and SACOL are dominated by coarse mode particles, while NUIST and Hong Kong PolyU are dominated by fine mode particles.

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 &gt; 96% for all the models (1 – 3).

Determination of Particulate Matters and Total Suspended Particles emitted from Incense Burning

Incense burning is an important ceremonial ritual in Buddhism. It is well recognized that incense smoke has negative health effects, which may be caused by the emission of submicron particles, including ultrafine and nanoparticles. Hence, in this study, the concentration of particulate matter (PM) and total suspended particles (TSP) emitted from incense burning were determined from 4 incense stick brands. The experiment was conducted in a room with a volume of approximately 146m3 using two instruments: an HV sampler and a Nano Sampler. The highest TSPs concentration from long sticks and short sticks were S1 (319.03 μg/m3) and N2 (439.75 μg/m3), respectively. High mass concentration was found in the ultrafine particle range for S2 (112.27 μg/m3) and N2 (117.30 μg/m3). In contrast, S1 and N1 exhibited high concentrations in the coarse particle mode at 79.28 μg/m3 and 86.75 μg/m3, respectively. Out of the 4 incense brands, N2 appeared to have the highest concentration in almost every particle range compared to the other 3 brands. Incense should be burned in a well-ventilated setting and try not to stay in the same place as the altar to reduce the risk of incense smoke exposure.