Aerosol Physicochemical Properties Research Articles

High-resolution physicochemical dataset of atmospheric aerosols over the Tibetan Plateau and its surroundings

Abstract. Atmospheric aerosol in the Tibetan Plateau (TP) and its surroundings has attracted significant scientific interest in recent decades due to its notable impacts on regional climatic and cryospheric changes, ecological and environmental security, and the hydrological cycle. However, our understanding of the atmospheric aerosol in this remote region is highly limited by the scarcity of available datasets owing to the extremely harsh natural conditions. This challenge has been mitigated in recent decades by establishing field observatories at typical sites within the TP and its surroundings. A continuous project initiated in 2015 aims to explore the properties and sources of atmospheric aerosols, as well as their regional differences, through multiple short-term intensive observations obtained across this vast region utilizing a suite of high-time-resolution online instruments. This paper presents a systematic and hourly scale dataset of aerosol physicochemical and optical properties at eight sites across the TP and its surroundings that is derived from the project. It includes size-resolved chemical compositions of submicron aerosols, high-resolution mass spectra and sources of organic aerosols, size distributions of particle number concentrations, particle light-scattering and light-absorption coefficients, particle light absorptions attributed to different carbonaceous substances including black carbon and brown carbon, and number concentrations of cloud condensation nuclei. In brief, atmospheric aerosols in these remote sites were all well mixed and highly aged, reflecting their dominant regional transport sources. However, the southern TP region exhibited high contributions of carbonaceous organic aerosols, neutralized bulk submicron aerosols, and a relatively high light-absorption capacity, whereas in the northern TP region, secondary inorganic species were the main contributors to the overall acidic submicron aerosols. Beyond providing insights into the regional differences in aerosol sources and properties across the TP and its surroundings, the datasets will also benefit simulations of aerosol radiative forcing and evaluations of interactions among different Earth system components in numerical models for this region. The datasets are accessible through the National Cryosphere Desert Data Center, Chinese Academy of Sciences (https://doi.org/10.12072/ncdc.NIEER.db2200.2022; Xu, 2022).

Aerosol delivery and spatiotemporal tissue distribution of hydroxychloroquine in rat lung

Inhalation enables the delivery of drugs directly to the lung, increasing the retention for prolonged exposure and maximizing the therapeutic index. However, the differential regional lung exposure kinetics and systemic pharmacokinetics are not fully known, and their estimation is critical for pulmonary drug delivery. The study evaluates the pharmacokinetics of hydroxychloroquine in different regions of the respiratory tract for multiple routes of administration. We also evaluated the influence of different inhaled formulations on systemic and lung pharmacokinetics by identifying suitable nebulizers followed by early characterization of emitted aerosol physicochemical properties. The salt- and freebase-based formulations required different nebulizers and generated aerosol with different physicochemical properties. An administration of hydroxychloroquine by different routes resulted in varied systemic and lung pharmacokinetics, with oral administration resulting in low tissue concentrations in all regions of the respiratory tract. A nose-only inhalation exposure resulted in higher and sustained lung concentrations of hydroxychloroquine with a lung parenchyma-to-blood ratio of 386 after 1440 min post-exposure. The concentrations of hydroxychloroquine in different regions of the respiratory tract (i.e., nasal epithelium, larynx, trachea, bronchi, and lung parenchyma) varied over time, indicating different retention kinetics. The spatiotemporal distribution of hydroxychloroquine in the lung is different due to the heterogeneity of cell types, varying blood perfusion rate, clearance mechanisms, and deposition of inhaled aerosol along the respiratory tract. In addition to highlighting the varied lung physiology, these results demonstrate the ability of the lung to retain increased levels of inhaled lysosomotropic drugs. Such findings are critical for the development of future inhalation-based therapeutics, aiming to optimize target site exposure, enable precision medicine, and ultimately enhance clinical outcomes.

Current challenges in the visibility improvement of urban Chongqing in Southwest China: From the perspective of PM2.5-bound water uptake property over 2015–2021

The visibility (VIS) improvement remains challenging such as in Southwest China, although the aerosol loading was reduced markedly. More in-depth understanding of interactions between visibility and aerosol physicochemical properties is required. This study systematically investigated mechanisms behind the interannual variation of low visibility at urban Chongqing from the aspect of PM2.5-bound optical enhancements over a relatively large timescale of 2015–2021. Results show that VIS <10 km frequently exceeded 50% in 2021 despite remarkable emission reductions since 2015, with the most severe challenge in visibility improvement faced in winter. Generally, the annual mean aerosol hygroscopicity and light extinction capacity were promoted during 2015–2021, as demonstrated by a higher optical enhancement factor (f(RH)), aerosol liquid water content per unit PM2.5 mass (i.e., ALWC/PM2.5), and dry mass extinction efficiency (MEEdry) observed for 2021 in comparison to previous years. A pronounced ascending trend existed in the annual mean fraction of nitrate (fNO3−), which even surpassed organics and sulfate to be the predominant composition in PM2.5. A similar evolution of fNO3− was observed during the visibility degradation specifically when VIS <10 km, highlighting the importance of highly hydrophilic inorganics in the haze formation. Given that the higher level of fNO3− normally introduced an elevated ALWC/PM2.5 which likely enhanced secondary aerosol formation (e.g., sulfate, nitrate, and secondary organics) via multiphase reactions, the combined effects could further exacerbate the visibility degradation particularly under highly humid and polluted conditions. Stricter controls such as on NOx and volatile organic precursors would be beneficial for the visibility improvement in China.

Iron content in aerosol particles and its impact on atmospheric chemistry.

Atmospheric aerosol effects on ecological and human health remain uncertain due to their highly complex and evolving nature when suspended in air. Atmospheric chemistry, global climate/oceanic and health exposure models need to incorporate more realistic representations of aerosol particles, especially their bulk and surface chemistry, to account for the evolution in aerosol physicochemical properties with time. (Photo)chemistry driven by iron (Fe) in atmospheric aerosol particles from natural and anthropogenic sources remains limited in these models, particularly under aerosol liquid water conditions. In this feature article, recent advances from our work on Fe (photo)reactivity in multicomponent aerosol systems are highlighted. More specifically, reactions of soluble Fe with aqueous extracts of biomass burning organic aerosols and proxies of humic like substances leading to brown carbon formation are presented. Some of these reactions produced nitrogen-containing gaseous and condensed phase products. For comparison, results from these bulk aqueous phase chemical studies were compared to those from heterogeneous reactions simulating atmospheric aging of Fe-containing reference materials. These materials include Arizona test dust (AZTD) and combustion fly ash particles. Also, dissolution of Fe and other trace elements is presented from simulated human exposure experiments to highlight the impact of aerosol aging on levels of trace metals. The impacts of these chemical reactions on aerosol optical, hygroscopic and morphological properties are also emphasized in light of their importance to aerosol-radiation and aerosol-cloud interactions, in addition to biogeochemical processes at the sea/ocean surface microlayer upon deposition. Future directions for laboratory studies on Fe-driven multiphase chemistry are proposed to advance knowledge and encourage collaborations for efficient utilization of expertise and resources among climate, ocean and health scientific communities.

Ultrafine particles in urban settings: A combined study of volatility and effective density revealed by VT-DMA-APM

Volatility and effective density of aerosol particles are complicatedly linked properties, undergoing dynamic temporal evolution in the ambient environment. However, the simultaneous investigation of these physicochemical characteristics remains unexplored in roadside environments that exhibit a significant proportion of motorcycles in the vehicle fleet - a common scenario in Southeast Asia. As such, we deployed an innovative in-situ measurement technique, specifically the Volatile Tandem Differential Mobility Analyzer and Aerosol Particle Mass Analyzer (VT-DMA-APM) system, to investigate ultrafine particles (UFPs) in an urban region of northern Taiwan. Our findings revealed that the UFPs predominant in this study area were largely soot aggregates interspersed with condensable materials. Traffic-related air pollutants (TRAPs), specifically condensable organic substances, emerged as key determinants of particle effective density and volatility. Intriguingly, the peculiar interrelation between aerosol physicochemical properties and particle size suggests that UFPs may represent an amalgamation of black carbon (BC) coated with condensable substances and non-BC-containing particles. We observed an inverse relationship between effective density and volatility, indicative of atmospheric aging processes. Moreover, concurrent measurements of Absorption Angstrom Exponent (AAE) and shape factor (Ks) provided valuable insights into variations in optical properties and morphology during aging. Peak AAE and minimal Ks values consistently occurred at noon, implying heightened particle aging during this period due to coating and morphological alterations.

Aerosol mass scattering efficiencies and single scattering albedo under high mass loading in Chiang Mai valley, Thailand

Aerosols amend the Earth's radiation budget by absorbing and scattering the incoming solar radiation. Severe air pollution episodes with high aerosol loading have continually occurred in northern Thailand for a long decade. This study comprehensively investigates the light scattering mechanism contingent on synchronous measurement of aerosol physicochemical and optical properties at Chiang Mai, the second largest city in Thailand per population, for two months during the spring of 2016. Daily mean values of the aerosol light scattering coefficient (σsca) at 550 nm ranged between 146 and 501 Mm−1. The scattering Ångström exponent (SAE450/700) ranged from 1.7 to 2.1, indicating a predominant contribution of finer particles to total light scattering. The mean mass scattering efficiency (MSE) of (NH4)2SO4, NH4NO3, organic matter (OM), dust, and others at 550 nm, estimated using a multilinear regression model were 3.3, 1.4, 4.4, 1.8, and 4.0 m2 g−1, respectively. The mean contribution of individual components to σsca was in the order of OM (66%) > Others (12%) > Dust (11%) > (NH4)2SO4 (9%) > NH4NO3 (2%). The mean (±SD) value of aerosol single scattering albedo at 550 nm wavelength was 0.80 ± 0.02 (range; 0.75–0.84), highlighting the presence of strongly absorbing aerosols. The total light absorption was primarily due to the mixture of organic and elemental carbons. The mean (±SD) MSE and mass absorption efficiency (MAE) of composite aerosols were 3.4 ± 0.4 m2 g−1 and 0.9 ± 0.1 m2 g−1, respectively. Notwithstanding the absorption, a simple radiative transfer model quantifies a negative top-of-atmosphere radiative forcing over Chiang Mai. These findings shed light on the impact of ambient aerosols on light scattering and urban climate. Moreover, our study offers a basic dataset to assess the visibility impairment in Chiang Mai.

MORPHOLOGY OF BIOAEROSOL PARTICLES IN THE SURFACE LAYER OF THE ATMOSPHERE OF MOSCOW METROPOLIS

Morphological properties of biogenic particles in the near-surface aerosol composition were studied by scanning electron microscopy in Moscow. We analyze the results of complex experiment conducted in 2019–2022 at the IAP RAS to study the variability of aerosol physico-chemical properties in a large city under various weather conditions. The main types of bioaerosol particles were determined, as well as their shape and size. For the first time, brochosomes were detected in the surface aerosol in Moscow during field aerosol observations.

Influence of aerosol physicochemical properties on CCN activation during the Asian winter monsoon at the summit of Mt. Lu, China

To better understand the characteristics of high-altitude aerosol (or condensation nuclei, CN) and cloud condensation nuclei (CCN) in East China during the Asian winter monsoon, a field campaign focused on aerosol and CCN was set up in the area of Mt. Lu during the period from 5 November to 10 December 2019. The features of CCN and CCN formation at Mt. Lu were analyzed. The CCN spectra at Mt. Lu belongs to a polluted continental type, which could be parameterized using N = 2498S0.31, with S denoting supersaturation. The average and standard deviation of the CCN (S = 0.4%) and CN concentrations were 1936 ± 1007 cm−3 and 3041 ± 1646 cm−3, respectively. The CCN activation fraction (AF) values are 0.43, 0.57, 0.64, 0.69, and 0.72 at S = 0.2%, S = 0.4%, S = 0.6%, S = 0.8% and S = 1%, respectively. The aerosol composition would be more important than aerosol size in determining CCN activation at Mt. Lu. The CCN (CN) number concentration had a clear diurnal variation with maximal and minimal values at 13:00 (12:00 and 18:00) and 07:00 (07:00), respectively. Nearly 68.7% of the air mass reaching Mt. Lu came from the northern area. The higher-sulfate-ratio air mass has a relatively high AF efficiency.

Regional organic matter and mineral dust are the main components of atmospheric aerosols over the Nam Co station on the central Tibetan Plateau in summer

The transport of air pollutants from areas surrounding the Tibetan Plateau (TP) has recently been studied. However, the major sources of atmospheric total suspended particulate matter (TSP) on the central TP remain unclear due to a lack of in-situ observations on aerosol physico-chemical properties. Therefore, to quantitatively investigate the physico-chemical properties and reveal the major sources of atmospheric aerosols, a comprehensive field campaign was conducted at the site of Nam Co from August 6 to September 11, 2020. Aerosol loading was low during the campaign with average TSP mass concentration, scattering coefficient at 550 nm, and absorption coefficient at 670 nm being 10.11 ± 5.36 μg m−3, 1.71 ± 1.36 Mm−1, and 0.26 ± 0.20 Mm−1, respectively. Organic matter (63.9%) and mineral dust (27.8%) accounted for most of the TSP mass concentrations. The average scattering Ångström exponent of 0.59 ± 0.14 reflected the influence of mineral dust, and the elemental fractions and the results of enrichment factor illustrated that crustal materials were the main contributors of mineral dust. The organic to elemental carbon ratio of 15.33 is probably caused by the aging that occurs during the transport of aerosols. The strong correlation between organic carbon and Ca2+ and the results of the electron microscopy analysis of single particles indicated that organic carbon and mineral dust had the same sources; however, the weak relation between mineral dust and wind speed indicated that local wind erosion was not the main contributor to the mineral dust. The potential source contribution function further illustrated that the summertime TSP in the central TP was mainly characterized by background biomass and mineral dust aerosols originating regionally from the ground within the TP.

Ambient Aerosol Is Physically Larger on Cloudy Days in Bondville, Illinois.

Particle chemical composition affects aerosol optical and physical properties in ways important for the fate, transport, and impact of atmospheric particulate matter. For example, hygroscopic constituents take up water to increase the physical size of a particle, which can alter the extinction properties and atmospheric lifetime. At the collocated AERosol RObotic NETwork (AERONET) and Interagency Monitoring of PROtected Visual Environments (IMPROVE) network monitoring stations in rural Bondville, Illinois, we employ a novel cloudiness determination method to compare measured aerosol physicochemical properties on predominantly cloudy and clear sky days from 2010 to 2019. On cloudy days, aerosol optical depth (AOD) is significantly higher than on clear sky days in all seasons. Measured Ångström exponents are significantly smaller on cloudy days, indicating physically larger average particle size for the sampled populations in all seasons except winter. Mass concentrations of fine particulate matter that include estimates of aerosol liquid water (ALW) are higher on cloudy days in all seasons but winter. More ALW on cloudy days is consistent with larger particle sizes inferred from Ångström exponent measurements. Aerosol chemical composition that affects hygroscopicity plays a determining impact on cloudy versus clear sky differences in AOD, Ångström exponents, and ALW. This work highlights the need for simultaneous collocated, high-time-resolution measurements of both aerosol chemical and physical properties, in particular at cloudy times when quantitative understanding of tropospheric composition is most uncertain.

The Ny-Ålesund Aerosol Cloud Experiment (NASCENT): Overview and First Results

Abstract The Arctic is warming at more than twice the rate of the global average. This warming is influenced by clouds, which modulate the solar and terrestrial radiative fluxes and, thus, determine the surface energy budget. However, the interactions among clouds, aerosols, and radiative fluxes in the Arctic are still poorly understood. To address these uncertainties, the Ny-Ålesund Aerosol Cloud Experiment (NASCENT) study was conducted from September 2019 to August 2020 in Ny-Ålesund, Svalbard. The campaign’s primary goal was to elucidate the life cycle of aerosols in the Arctic and to determine how they modulate cloud properties throughout the year. In situ and remote sensing observations were taken on the ground at sea level, at a mountaintop station, and with a tethered balloon system. An overview of the meteorological and the main aerosol seasonality encountered during the NASCENT year is introduced, followed by a presentation of first scientific highlights. In particular, we present new findings on aerosol physicochemical and molecular properties. Further, the role of cloud droplet activation and ice crystal nucleation in the formation and persistence of mixed-phase clouds, and the occurrence of secondary ice processes, are discussed and compared to the representation of cloud processes within the regional Weather Research and Forecasting Model. The paper concludes with research questions that are to be addressed in upcoming NASCENT publications.

Effects of Atmospheric Aging Processes on Nascent Sea Spray Aerosol Physicochemical Properties.

The effects of atmospheric aging on single-particle nascent sea spray aerosol (nSSA) physicochemical properties, such as morphology, composition, phase state, and water uptake, are important to understanding their impacts on the Earth's climate. The present study investigates these properties by focusing on the aged SSA (size range of 0.1-0.6 μm) and comparing with a similar size range nSSA, both generated at a peak of a phytoplankton bloom during a mesocosm study. The aged SSAs were generated by exposing nSSA to OH radicals with exposures equivalent to 4-5 days of atmospheric aging. Complementary filter-based thermal optical analysis, atomic force microscopy (AFM), and AFM photothermal infrared spectroscopy were utilized. Both nSSA and aged SSA showed an increase in the organic mass fraction with decreasing particle sizes. In addition, aging results in a further increase of the organic mass fraction, which can be attributed to new particle formation and oxidation of volatile organic compounds followed by condensation on pre-existing particles. The results are consistent with single-particle measurements that showed a relative increase in the abundance of aged SSA core-shells with significantly higher organic coating thickness, relative to nSSA. Increased hygroscopicity was observed for aged SSA core-shells, which had more oxygenated organic species. Rounded nSSA and aged SSA had similar hygroscopicity and no apparent changes in the composition. The observed changes in aged SSA physicochemical properties showed a significant size-dependence and particle-to-particle variability. Overall, results showed that the atmospheric aging can significantly influence the nSSA physicochemical properties, thus altering the SSA effects on the climate.

Initial pH Governs Secondary Organic Aerosol Phase State and Morphology after Uptake of Isoprene Epoxydiols (IEPOX).

Aerosol acidity increases secondary organic aerosol (SOA) formed from the reactive uptake of isoprene-derived epoxydiols (IEPOX) by enhancing condensed-phase reactions within sulfate-containing submicron particles, leading to low-volatility organic products. However, the link between the initial aerosol acidity and the resulting physicochemical properties of IEPOX-derived SOA remains uncertain. Herein, we show distinct differences in the morphology, phase state, and chemical composition of individual organic-inorganic mixed particles after IEPOX uptake to ammonium sulfate particles with different initial atmospherically relevant acidities (pH = 1, 3, and 5). Physicochemical properties were characterized via atomic force microscopy coupled with photothermal infrared spectroscopy (AFM-PTIR) and Raman microspectroscopy. Compared to less acidic particles (pH 3 and 5), reactive uptake of IEPOX to the most acidic particles (pH 1) resulted in 50% more organosulfate formation, clearer phase separation (core-shell), and more irregularly shaped morphologies, suggesting that the organic phase transitioned to semisolid or solid. This study highlights that initial aerosol acidity may govern the subsequent aerosol physicochemical properties, such as viscosity and morphology, following the multiphase chemical reactions of IEPOX. These results can be used in future studies to improve model parameterizations of SOA formation from IEPOX and its properties, toward the goal of bridging predictions and atmospheric observations.

Role of Aerosol Physicochemical Properties on Aerosol Hygroscopicity and Cloud Condensation Nuclei Activity in a Tropical Coastal Atmosphere

Role of Aerosol Physicochemical Properties on Aerosol Hygroscopicity and Cloud Condensation Nuclei Activity in a Tropical Coastal Atmosphere

Influence of aerosol physico-chemical properties on cloud microphysical parameters perceived using in-situ high altitude observations

Variability in cloud microphysical parameters, aerosol physicochemical properties and their relationship were studied using in-situ ground observations from a high altitude site in Western Ghats, India, during monsoon season. Cloud microphysical parameters, such as cloud droplet number concentration (CDNC), liquid water content (LWC), and effective diameter (ED), have been analyzed. Aerosol–CCN (cloud condensation nuclei) number concentration and mass concentration of non-refractory particulate matter (NR-PM1) during summer monsoon also showed day to day and monthly variation. Cloud droplet size distribution (CDSD) showed a bimodal spectrum with two prominent peaks i.e. in 3–10 μm and 12–22 μm size ranges. The estimated spectral width of CDSD (σ) broadly varied from 0 to 4 μm and the effective radius ratio (β) from 0.6–1.8. Further, the effect of aerosol on cloud microphysical parameters and CDSD has been investigated. There was an apparent variation in CCN super saturation spectrum, aerosol chemical composition, and cloud microphysics during high and low aerosol loading daysThe aerosol chemical composition showed a higher sulphate and ammonium (organics) contribution during low (high) aerosol loading days. CCN concentration and CDNC (ED) were higher (less) during high aerosol days and vice versa during low aerosol days. A review of microphysical characteristics of monsoon clouds over various locations of the Indian region has shown that this is the first such report that provides observational evidence of how variation in aerosol physical and chemical properties affects the CCN and cloud properties derived explicitly from long-term ground-based observations.

Characterisation of the Manchester Aerosol Chamber facility

Abstract. This study describes the design of the Manchester Aerosol Chamber (MAC), initially developed in 2005 and presents for the first time its comprehensive characterisation. The MAC is designed to investigate multi-phase chemistry and the evolution of aerosol physico-chemical properties from the real-world emissions (e.g. diesel engine, plants) or of secondary organic aerosol (SOA) produced from pure volatile organic compounds (VOCs). Additionally, the generated aerosol particles in the MAC can be transferred to the Manchester Ice Cloud Chamber (MICC), which enables investigation of cloud formation in warm, mixed-phase, and fully glaciated conditions (with temperature, T, as low as −55 ∘C). The MAC is an 18 m3 fluorinated ethylene propylene (FEP) Teflon chamber with the potential to conduct experiments at controlled temperature (15–35 ∘C) and relative humidity (RH; 25 %–80 %) under simulated solar radiation or dark conditions. Detailed characterisations were conducted at common experimental conditions (25 ∘C, 50 % RH) for actinometry and determination of background contamination, wall losses of gases (NO2, O3, and selected VOCs), aerosol particles at different sizes, chamber wall reactivity, and aerosol formation. In addition, the influences of chamber contamination on the wall loss rate of gases and particles and the photolysis of NO2 were estimated.

Combining POLDER-3 satellite observations and WRF-Chem numerical simulations to derive biomass burning aerosol properties over the southeast Atlantic region

Abstract. Aerosol absorption is a key property to assess the radiative impacts of aerosols on climate at both global and regional scales. The aerosol physico-chemical and optical properties remain not sufficiently constrained in climate models, with difficulties to properly represent both the aerosol load and their absorption properties in clear and cloudy scenes, especially for absorbing biomass burning aerosols (BBA). In this study we focus on biomass burning (BB) particle plumes transported above clouds over the southeast Atlantic (SEA) region off the southwest coast of Africa, in order to improve the representation of their physico-chemical and absorption properties. The methodology is based on aerosol regional numerical simulations from the WRF-Chem coupled meteorology–chemistry model combined with a detailed inventory of BB emissions and various sets of innovative aerosol remote sensing observations, both in clear and cloudy skies from the POLDER-3/PARASOL space sensor. Current literature indicates that some organic aerosol compounds (OC), called brown carbon (BrOC), primarily emitted by biomass combustion absorb the ultraviolet-blue radiation more efficiently than pure black carbon (BC). We exploit this specificity by comparing the spectral dependence of the aerosol single scattering albedo (SSA) derived from the POLDER-3 satellite observations in the 443–1020 nm wavelength range with the SSA simulated for different proportions of BC, OC and BrOC at the source level, considering the homogeneous internal mixing state of particles. These numerical simulation experiments are based on two main constraints: maintaining a realistic aerosol optical depth both in clear and above cloudy scenes and a realistic BC/OC mass ratio. Modelling experiments are presented and discussed to link the chemical composition with the absorption properties of BBA and to provide estimates of the relative proportions of black, organic and brown carbon in the African BBA plumes transported over the SEA region for July 2008. The absorbing fraction of organic aerosols in the BBA plumes, i.e. BrOC, is estimated at 2 % to 3 %. The simulated mean SSA are 0.81 (565 nm) and 0.84 (550 nm) in clear and above cloudy scenes respectively, in good agreement with those retrieved by POLDER-3 (0.85±0.05 at 565 nm in clear sky and at 550 nm above clouds) for the studied period.

Investigation of physico-chemical characteristics and associated CCN activation for different combustion sources through Chamber experiment approach

The aerosol physico-chemical properties along with their CCN activation characteristics were studied for different combustion source types such as Diesel Generator (DG), wood, leaf, charcoal, grass and cow dung through chamber-based experiment. Aethalometer (AE-33), High resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS), scanning mobility particle sizer (SMPS) and cloud condensation nuclei (CCN) counter were connected in line to derive the absorption properties, chemical composition, size distribution and CCN number concentrations respectively. Angstrom absorption exponent (AAE) and Angstrom absorption exponent ratio (AAER) were estimated utilizing the Aethalometer data. The analysis reveals that the DG emission was associated with the lowest AAE value (0.92) and the AAE value was highest for cow dung emissions (2.15). AAER, a ratio of AAE at longer wavelengths (660–950 nm) to smaller wavelengths (370-660 nm), showed value < 1 for most of biomass burning types, whereas, the AAER value was >1 for DG emission. The chemical composition data reveals that the organics contribute more than 90% to most of the combustion sources except charcoal, for which the organic contribution was only 78%. High-resolution data analysis reveals that leaf burning was associated with the highest f44 fraction indicating the emitted organic aerosols contain more oxygen. The chemical composition derived hygroscopicity parameter (κ) was estimated to be highest for charcoal emissions and lowest for diesel and cooking emissions. Hygroscopicity parameter (κ) was also evaluated utilizing CCN and SMPS data. The CCN activation and size distribution analysis revealed that the CCN activation of cow dung was highest at 0.1% and 0.3% SS, this is associated with the higher geometric mean diameter (GMD) of emitted aerosols, indicating the importance of size compared to the chemical composition. The activation fraction of charcoal emission was found to be higher than DG emission in these super-saturations, indicating the importance of hygroscopicity in addition to size for governing the CCN activation when the GMD is on the lower side.

Characterization of aerosol number size distributions and their effect on cloud properties at Syowa Station, Antarctica

Abstract. We took aerosol measurements at Syowa Station, Antarctica, to characterize the aerosol number–size distribution and other aerosol physicochemical properties in 2004–2006. Four modal structures (i.e., mono-, bi-, tri-, and quad-modal) were identified in aerosol size distributions during measurements. Particularly, tri-modal and quad-modal structures were associated closely with new particle formation (NPF). To elucidate where NPF proceeds in the Antarctic, we compared the aerosol size distributions and modal structures to air mass origins computed using backward trajectory analysis. Results of this comparison imply that aerosol size distributions involved with fresh NPF (quad-modal distributions) were observed in coastal and continental free troposphere (FT; 12 % of days) areas and marine and coastal boundary layers (1 %) during September–October and March and in coastal and continental FT (3 %) areas and marine and coastal boundary layers (8 %) during December–February. Photochemical gaseous products, coupled with ultraviolet (UV) radiation, play an important role in NPF, even in the Antarctic troposphere. With the existence of the ozone hole in the Antarctic stratosphere, more UV radiation can enhance atmospheric chemistry, even near the surface in the Antarctic. However, linkage among tropospheric aerosols in the Antarctic, ozone hole, and UV enhancement is unknown. Results demonstrated that NPF started in the Antarctic FT already at the end of August–early September by UV enhancement resulting from the ozone hole. Then, aerosol particles supplied from NPF during periods when the ozone hole appeared to grow gradually by vapor condensation, suggesting modification of aerosol properties such as number concentrations and size distributions in the Antarctic troposphere during summer. Here, we assess the hypothesis that UV enhancement in the upper troposphere by the Antarctic ozone hole modifies the aerosol population, aerosol size distribution, cloud condensation nuclei capabilities, and cloud properties in Antarctic regions during summer.

Emissions of soot, PAHs, ultrafine particles, NO x, and other health relevant compounds from stressed burning of candles in indoor air

Burning candles release a variety of pollutants to indoor air, some of which are of concern for human health. We studied emissions of particles and gases from the stressed burning of five types of pillar candles with different wax and wick compositions. The stressed burning was introduced by controlled fluctuating air velocities in a 21.6 m3 laboratory chamber. The aerosol physicochemical properties were measured both in well-mixed chamber air and directly above the candle flame with online and offline techniques. All candles showed different emission profiles over time with high repeatability among replicates. The particle mass emissions from stressed burning for all candle types were dominated by soot (black carbon; BC). The wax and wick composition strongly influenced emissions of BC, PM2.5, and particle-phase polycyclic aromatic hydrocarbons (PAHs), and to lower degree ultrafine particles, inorganic and organic carbon fraction of PM, but did not influence NOx, formaldehyde, and gas-phase PAHs. Measurements directly above the flame showed empirical evidence of short-lived strong emission peaks of soot particles. The results show the importance of including the entire burn time of candles in exposure assessments, as their emissions can vary strongly over time. Preventing stressed burning of candles can reduce exposure to pollutants in indoor air.