Properties Of Atmospheric Aerosols Research Articles

Ion-molecule interactions enable unexpected phase transitions in organic-inorganic aerosol.

Atmospheric aerosol particles are commonly complex, aqueous organic-inorganic mixtures, and accurately predicting the properties of these particles is essential for air quality and climate projections. The prevailing assumption is that aqueous organic-inorganic aerosols exist predominately with liquid properties and that the hygroscopic inorganic fraction lowers aerosol viscosity relative to the organic fraction alone. Here, in contrast to those assumptions, we demonstrate that increasing inorganic fraction can increase aerosol viscosity (relative to predictions) and enable a humidity-dependent gel phase transition through cooperative ion-molecule interactions that give rise to long-range networks of atmospherically relevant low-mass oxygenated organic molecules (180 to 310 Da) and divalent inorganic ions. This supramolecular, ion-molecule effect can drastically influence the phase and physical properties of organic-inorganic aerosol and suggests that aerosol may be (semi)solid under more conditions than currently predicted. These observations, thus, have implications for air quality and climate that are not fully represented in atmospheric models.

Performance Assessment of Portable Optical Particle Spectrometer (POPS).

Accurate representation of atmospheric aerosol properties is a long-standing problem in atmospheric research. Modern pilotless aerial systems provide a new platform for atmospheric in situ measurement. However, small airborne platforms require miniaturized instrumentation due to apparent size, power, and weight limitations. A Portable Optical Particle Spectrometer (POPS) is an emerged instrument to measure ambient aerosol size distribution with high time and size resolution, designed for deployment on a small unmanned aerial system (UAS) or tethered balloon system (TBS) platforms. This study evaluates the performance of a POPS with an upgraded laser heater and additional temperature sensors in the aerosol pathway. POPS maintains its performance under different environmental conditions as long as the laser temperature remains above 25 °C and the aerosol flow temperature inside the optical chamber is 15 °C higher than the ambient temperature. The comparison between POPS and an Ultra-High Sensitivity Aerosol Spectrometer (UHSAS) suggests that the coincidence error is less than 25% when the number concentration is less than 4000 cm−3. The size distributions measured by both of them remained unaffected up to 15,000 cm−3. While both instruments’ sizing accuracy is affected by the aerosol chemical composition and morphology, the influence is more profound on the POPS.

Physical and chemical properties of atmospheric aerosols in Moscow and its suburb for climate assessments

The paper presents results of experimental study of the physicochemical properties of surface aerosols in the Moscow region in the summer of 2019. Microphysical parameters, mass concentration and elemental composition of submicron and micron aerosol particles are considered, and their morphological structure is described. The features of variability of aerosol characteristics under atypical weather conditions prevailing in June-July 2019 are shown. The spatial distribution of the elemental composition of aerosols is established, a significant degree of their enrichment with heavy metals and metalloids is revealed. Geochemical analysis of aerosols and soils in Moscow was performed, and the coefficients of local aerosol concentration were calculated. The obtained experimental data will be useful for the refinement and verification of climate models.

Atmospheric aerosol and black carbon optical properties and associated radiative forcing under haze conditions

The optical properties and radiative forcing of atmospheric aerosol (ARF) and black carbon (BC) aerosol (BCRF) in ultraviolet (UV), visible (VIS), near-infrared (NIR), and shortwave (SW) spectra were investigated under haze conditions based on the observations of the Aethalometer and sun-sky radiometer and simulations from libRadtran. The results show that the BC concentrations increased greatly from 2.73 μg/m3 under clear-air conditions to 7.95 μg/m3 under severe haze conditions, while BC aerosol optical depth (AOD) increased from 0.025 to 0.092. A high correlation (R2=0.62) was found between BC AOD and absorbing aerosol optical depth (AAOD) derived from the sun-sky radiometer. The BCRF in SW (BCRFSW) varied from -10.20 W/m2 under clear-air conditions to -25.40 W/m2 under severe hazy conditions. However, its fraction in ARF (ARFSW) decreased from 19% to 17% simultaneously, which is mainly related to the decrease of the ratio of BC AOD to AOD. The fraction of ARF in VIS in ARFSW decreased from 56.3% under clear-air conditions to 50.5% under severe haze conditions, while the fraction of BCRF in VIS in BCRFSW was much larger, and increased from 72.9% to 73.8%. The BCRF efficiency (BCRFE) was much larger than ARF efficiency (ARFE), and both of them decreased with the development of haze. The ARFE in SW decreased from -173.84 W/m2 under clear-air conditions to -112.75 W/m2 under severe haze conditions while BCRFESW varied from -482.50 W/m2 to -321.88 W/m2. The decrease of ARFE and BCRFE is related to the increase of aerosol loading and asymmetry factor (ASY). The ASY increased and the forward scattering was enhanced with the development of haze due to the hygroscopic growth of aerosol particles, which reduced the extinction efficiency of aerosols including BC on solar radiation and the cooling effect on the surface.

Aerosol Direct Radiative Effects over China Based on Long-Term Observations within the Sun–Sky Radiometer Observation Network (SONET)

To investigate aerosol radiative effects, the Sun–Sky Radiometer Observation Network (SONET) has performed long-term observations of columnar atmospheric aerosol properties at 20 distributed stations around China. The aerosol direct radiative forcing (RF) and efficiency (RFE, the rate at which the atmosphere is forced per unit of aerosol optical depth) were estimated using radiative transfer model simulations based on the ground-based observations dating back to 2009. Results of multi-year monthly average RF illustrated that: the dust-dominant aerosol population at arid and semi-arid sites exerted moderate cooling effects (−8.0~−31.2 W/m2) at the top and bottom of atmosphere (TOA and BOA); RF at continental background site was very weak (−0.8~−2.9 W/m2); fine-mode dominant aerosols at urban and suburban sites exerted moderate cooling effects (−9.3~−24.1 W/m2) at TOA but more significant cooling effects (−19.4~−50.6 W/m2) at BOA; RF at coastal sites was comparable with values of urban sites (−5.5~−19.5 W/m2 at TOA, and −15.6~−44.6 W/m2 at BOA), owing to combined influences by marine and urban–industrial aerosols. Differences between RFE at TOA and BOA indicated that coarse-mode dominant aerosols at arid, semi-arid, and continental background sites were less efficient to warm the atmosphere; but fine-mode dominant aerosols at urban, suburban, and coastal sites were shown to be more efficient to heat the atmosphere.

Observation of Aerosol Optical Properties and New Particle Formation in the Yangtze River Delta

In a recent field campaign focused on air quality study, aerosol optical properties, particle number concentration, and PM2.5 components were monitored in Changzhou, Jiangsu Province, from May 27 to June 27, 2019. An array of instruments were deployed that included scanning mobility particle size spectrometer (SMPS), aethalometer (AE33), cavity attenuation phase shift single albedo monitor (CAPS-ALB), monitor for aerosols and gases in ambient air (MARGA) and RT-4 organic carbon/elemental carbon (OC/EC) carbon analyzer to study the ① changes in chemical composition and optical parameters of the new particles generated during the campaign period. ② comparison of the aerosol extinction coefficient recorded by these instruments and measured value in the reconstruction of IMPROVE (interagency monitoring of protected visual environment) and the calculated coefficient using MIE theory model were carried out. During the entire campaign, two new particle generation events were observed and also found that the particle size continued to increase from 4 nm to 64 nm. It was monitored that in the initial stage of new particle generation, sulfate contributed greatly. The measured average aerosol extinction coefficient during the period of particle generation, using these instruments was 95.40 Mm-1, while the average aerosol extinction reconstruction using the IMPROVE model was observed to be 140.20 Mm-1. The theoretical calculations based on Mie theory model yielded an average extinction coefficient of 93.54 Mm-1. It was found that the average aerosol extinction in Changzhou is lower than the average value of the urban aerosol extinction coefficient, which is measured to be 300 Mm-1 in China, during this period. The deployment of multiple instruments in a single campaign is more desirable because the combination of all observations helped in better characterization of the physicochemical properties of ambient aerosols from various aspects, including particle size spectrum and chemical composition.

Impact of aging process on atmospheric black carbon aerosol properties and climate effects

Black carbon (BC) is a key driver of global warming, exerting a strong but highly uncertain effect on the global climate. A key challenge of quantifying BC’s radiative effect is predicting the impact of aging process on BC’s properties. BC is mainly emitted from the incomplete combustion of fossil fuel and biomass burning. After being emitted, it undergoes complex chemical and physical transformations in the atmosphere, through condensation, coagulation and heterogeneous oxidation, which is referred to as BC aging. During aging, BC is gradually coated by other chemical species, which dramatically affects BC properties and alters the corresponding climate effects. The objective of this review is to discuss the current knowledge of BC aging from both laboratory and field measurements. This review first summarizes the methods used in the laboratory experiments and field observations. Then it reviews the effects of aging process on BC mixing state, which comprises both morphology and chemical composition. On this basis, changes to BC light absorption, hygroscopicity, cloud condensation nuclei (CCN) and ice nucleation (IN) activity during the aging process are discussed; these properties are closely related to BC climate effects. Laboratory studies on BC aging are always conducted using single-precursor systems, which do not capture the complex composition of the real atmosphere. In field studies, some state-of-the-art online instruments have been deployed to measure BC properties. However, since the field studies are usually conducted at fixed stations, it is difficult to dynamically track the entire BC aging process. Atmospheric aging process converts BC particles from externally mixed to internally mixed, with other chemical species coated on them. The morphology evolution in the aging process contains three stages: void filling, collapse and subsequent growth, which results in BC morphology changing from the initially chain-like shapes to spherical core-shell structures. The chemical composition of coatings is affected by both emission source and extent of aging, showing an increasing proportion of secondary species during the aging process. BC light absorption is enhanced because of coatings that accumulate during aging. However, the absorption enhancement factors reported in previous studies show large discrepancy because of differences in aging degree, morphology and chemical composition. The particle-to-particle heterogeneity in mixing state can also lead to different enhancement factors for particle populations. Along with the enhancement of light absorption, BC particles hygroscopicity and CCN activity are also enhanced during aging process. However, observational evidence is still lacking. The IN activity of BC is still an open question, and whether aging process enhances or suppresses the IN activity of BC is still debatable. Based on this review of previous studies, we recommend further research on the following topics: (1) Characterize the aging process for BC from different emission sources under realistic combustion conditions. (2) Identify the key factors affecting BC aging in various atmospheric environments. (3) Explore the role of BC particles in regional air pollution. (4) Conduct further studies on the interaction between BC and cloud formation.

Optical properties of atmospheric aerosol over Cape Town, Western Cape of South Africa: Role of biomass burning

The optical characteristics of atmospheric aerosol are vital in the determination of the regional climate trend. Biomass burning is typically known to influence aerosol optical characteristics. Following the incessant biomass burning and the recent drop in precipitation over Western Cape, the aerosol optical properties with a focus on the impact of biomass burning are studied over Cape Town using data from AERONET (Aerosol Robotic Network) and MODIS (Moderate Resolution Imaging Spectroradiometer). In general terms, measurements from both platforms significantly agree on the estimates of aerosol optical depth (AOD) and water vapor content (WVC). The mean AOD 0.075 (± 0.022) and Ångström exponent (AE) 0.63 (± 0.19) derived from AERONET demonstrate the dominance of coarse mode aerosol typical of maritime aerosol. Similarly, aerosol particle size distributions display the predominance of coarse mode particles. However, the derived refractive index is more representative of urban-industrial aerosol. Also, estimated back-trajectories show that more than 70% of the aerosol particles over the region originate over the ocean. Atmospheric vapor increases from winter to summer and mainly influenced by air temperature, supersaturation level, and absorbing aerosol. Furthermore, two significant sources accounted for biomass burning related to high AOD values: local biomass burning and regionally transported aged smoke majorly from elsewhere in Sothern Africa.

Optical properties of atmospheric aerosol over Cape Town, Western Cape of South Africa: Role of biomass burning

The optical characteristics of atmospheric aerosol are vital in the determination of regional climate trends. Biomass burning is typically known to influence aerosol optical characteristics. Following the incessant biomass burning and the recent drop in precipitation over Western Cape, aerosol optical properties with a focus on the impact of biomass burning are studied over Cape Town using data from the Aerosol Robotic Network (AERONET) and the Moderate Resolution Imaging Spectroradiometer (MODIS). In general terms, measurements from both platforms significantly agree on the estimates of aerosol optical depth (AOD) and water vapor content. The mean AOD (0.075 ± 0.022) and the Angstrom exponent (0.63 ± 0.19) derived from AERONET demonstrate the dominance of coarse mode aerosol typical of maritime aerosol. Similarly, aerosol particle size distributions display the predominance of coarse mode particles. However, the derived refractive index is more representative of urban-industrial aerosol. Also, estimated back-trajectories show that more than 70% of the aerosol particles over the region originate over the ocean. Atmospheric vapor increases from winter to summer, mainly influenced by air temperature, supersaturation level, and absorbing aerosol. Furthermore, two significant sources accounted for biomass burning related to high AOD values: local biomass burning and regionally transported aged smoke majorly from elsewhere in Sothern Africa.

Response of fine aerosol nitrate chemistry to Clean Air Action in winter Beijing: Insights from the oxygen isotope signatures

The implementation of Clean Air Actions improved air quality in Beijing, and the mass loadings of PM2.5 and numerous gaseous precursors decreased considerably. However, concentrations of particulate nitrate (p-NO3) changed slightly in wintertime aerosol and its mass fraction increased from 11.3% in 2013 to 29.8% in 2018. Therefore, understanding the characteristics of nitrate chemistry is imperative for controlling the aerosol pollution in the context of emission reductions in China. To this end, the properties of aerosol, chemistry of nitrate during the past winter seasons of Beijing (2013–2017) were investigated. Results indicated that nitrate remained entirely in the particle phase. The weak response of p-NO3− to NOx emission reduction (~17.9%) was attributed to the enhanced gaseous HNO3 formation. The oxygen isotopic signatures of p-NO3− (δ18O-NO3−) in winter 2017 of Beijing (75.0 ± 12.6‰) was significantly lower than that in winter 2014 (82.6 ± 12.7‰), but comparable with that in Puding (77.3 ± 4.6‰, background site of Southwest China) and Nanning (72.9 ± 4.9‰, urban site in South China) of winter 2017. We inferred an increased photochemistry activity in the formation of winter p-NO3− in Beijing recently. The enhanced photochemistry was mainly due to the increased photolysis of HONO, a major source of atmospheric hydroxyl radical (OH) in polluted urban environment. The considerable generated HONO was attributed to the photolysis of p-NO3− according to δ18O isotopic evidence. The present study implied that the response of aerosol species to emission reductions and their feedbacks associated with the atmospheric oxidants and aerosol properties were complex and needed further investigations.

The Optical Properties of Aerosols at the Summit of Mount Tai in May and June and the Retrieval of the Complex Refractive Index

To study the optical properties of background atmospheric aerosols in East China, we carried out observations of the physical, chemical and optical properties of atmospheric aerosols at the summit of Mount Tai (Mt. Tai, 1533.7 m above sea level) from 13 May to 25 June 2017. The results show that the average scattering coefficient ( σ sca , 550 ) at 550 nm of the aerosols at the summit of Mt. Tai is 40.3 Mm−1, and the average absorption coefficient ( σ abs , 550 ) at 550 nm is 16.0 Mm−1. The complex refractive index of aerosols is a key parameter for aerosol retrieval and modeling. There are few studies on the equivalent complex refractive index of aerosol in the Taishan area. We calculated the aerosol equivalent complex refractive index using the observed aerosol scattering coefficients, absorption coefficients and particle size distribution data, providing more data support for future modeling in this region. The real part (n) of the complex refractive index at 550 nm of aerosol ranges from 1.31 to 1.98 (mostly under 1.50), with an average value of 1.38, while the imaginary part (k) ranges from 0.014 to 0.251 (less than 0.10 for over 95% samples), with an average value of 0.040. The analysis of the n and k of the aerosol average complex refractive index shows that the scattering properties of the aerosols at the summit of Mt. Tai are relatively weak and the absorption properties are relatively strong when compared with those of other kinds of aerosols. The k of the aerosol complex refractive index at the summit of Mt. Tai has strong correlations with the wind speed, temperature, as revealed by the correlation analysis.

Research on BP network for retrieving extinction coefficient from Mie scattering signal of lidar

Abstract Mie lidar is a powerful tool for detecting the optical properties of atmospheric aerosols. However, there are two unknown parameters in the Mie lidar equation: the extinction coefficient and the backscattering coefficient. In the common methods for solving the equation, it is necessary to make assumptions about the relationship between the two unknown parameters. These assumptions will reduce the detection precision of extinction coefficient. In view of this, the back propagation (BP) neural network is used to retrieve extinction coefficient from the Mie scattering signal of lidar. Firstly, the structure and main parameters of the BP network are designed according to the practical application. In order to improve the convergence speed and prevent falling into local minima, the initial weights and thresholds of BP network are optimized by genetic algorithm (GA). Then the GA-BP network is trained with Mie scattering signal and the extinction coefficient retrieved by Raman method. Thus the mathematical relationship between Mie scattering signal and the extinction coefficient is stored in the BP network. The trained GA-BP network is then used to retrieve the extinction coefficient from Mie scattering signal in different conditions and the applicability of the GA-BP network is researched. The research will promote the development of Mie lidar retrieving algorithm.

Long-term (2008–2018) aerosol properties and radiative effect at high-altitude sites over western trans-Himalayas

Analysis of the climatology of aerosol properties is performed over Hanle (4500 m) and Merak (4310 m), two remote-background sites in the western trans-Himalayas, based on eleven years (2008–2018) of sun/sky radiometer (POM-01, Prede) measurements. The two sites present very similar atmospheric conditions and aerosol properties allowing us to examine them as continuous single-data series. The annual average aerosol optical depth at 500 nm (AOD500) is 0.04 ± 0.03, associated with an Ångström exponent (AE440–870) of 0.58 ± 0.35 and a single scattering albedo (SSA500) of 0.95 ± 0.05. AOD500 exhibits higher values in May (~0.07) and lower in winter (~0.03), while AE400–870 minimizes in spring, indicating influence by coarse-mode dust aerosols, either emitted regionally or long-range transported. The de-convolution of AOD500 into fine and coarse modes justifies the aerosol seasonality and sources, while the marginal diurnal variation in all aerosol properties reveals a weak influence from local sources, except for some few aerosol episodes. The aerosol-volume size distribution presents a mode value at ~10 μm with secondary peaks at accumulation (~ 2 μm) and fine modes (~0.03 μm) and low variability between the seasons. A classification of the aerosol types based on the fine-mode fraction (FMF) vs. SSA500 relationship reveals the dominance of aerosols in the FMF range of 0.4–0.6, characterized as mixed (39%), followed by fine aerosols with high scattering efficiency (26%), while particles related to dust contribute ~21%, with low fractions of fine-absorbing aerosols (~13%). The aerosol radiative forcing (ARF) estimates reveal a small cooling effect at the top of the atmosphere (−1.3 Wm−2), while at the surface, the ARF ranges from −2 Wm−2 to −6 Wm−2 on monthly basis. The monthly-mean atmospheric radiative forcing (~1 to 4 Wm−2) leads to heating rates of 0.04 to 0.13 K day−1. These ARF values are higher than the global averages and may cause climate implications over the trans-Himalayan region.

Study on the characteristics of black carbon during atmospheric pollution conditions in Beijing

Black carbon (BC), not only has a negative impact on human health, but also contributes to visibility degradation and the attenuation of solar radiation due to light absorption. In this paper, we investigated the variations of BC concentration, BC optical characteristics and its effects on the physical and optical properties of atmospheric aerosols based on AERONET data during atmospheric pollution conditions in Beijing from 2012 to 2017. The results indicated that the average annual ground-level BC concentration and BC/PM2.5 were 8.9 μg m−3 and 6.7%, respectively, from 2012 to 2017 during atmospheric pollution conditions in Beijing. The annual mean ground-level BC concentration showed weak variation, but the monthly variation was pronounced during atmospheric pollution conditions. Moreover, the BC column concentration had a higher correlation with absorptive aerosol optical thickness (AAOT) at 870 nm (R2 = 0.93) than 440 nm (R2 = 0.73). The difference in AAOT between 440 nm and 870 nm was more significant under high BC column concentration. The seasonal variation of the BC column concentration that contributed to the AAOT at 870 nm displayed a consistent monthly average variation tendency. The BC column concentrations were divided into three segments of low, moderate, and high according to the results of the approximately normal distribution of the BC column concentration. Compared with high BC concentration, the single scattering albedo (SSA) and asymmetry parameter were enhanced by 0.05 and 0.04 in low BC concentrations, respectively. On the contrary, the fine mode fraction (FMF) was dropped by 12.5% in low BC concentrations. A higher BC concentration contributed to the enhancement in the AAOT and the extinction ratio of the fine mode aerosol. Meanwhile, the atmospheric particles' forward scattering ability was also attenuated under a high BC concentration.

Atmospheric aerosol properties at a semi-rural location in southern India: particle size distributions and implications for cloud droplet formation

Particle number size distributions in the diameter range of 5 nm–34 µm were measured in tropical southern India during the transition season from May (pre-monsoon) to June–July (monsoon). Averaged over the entire measurement period, the particle number size distributions were bimodal with a total particle number concentration of NTot = (4.5 ± 2.7) × 103 cm−3 (arithmetic mean ± standard deviation). The ratio of Aitken to accumulation mode particle number concentrations (NAit/NAcc) ranged from 1.06 to 2.07, increasing from May to June–July due to a pronounced decrease in the accumulation mode particles with the onset of the monsoon. Cloud condensation nuclei concentrations at 0.4% supersaturation (CCN0.4) were calculated under the assumption of an average continental hygroscopicity parameter of κ = 0.3. The calculated CCN0.4 concentrations are mostly sensitive to variations in NAcc and vary accordingly between the May and June–July. Using a cloud parcel model, we investigated the formation of cloud droplets using the measured average particle number size distributions, updraft velocities up to 20 m s−1, and initial aerosol particle number concentrations up to 25,000 cm−3. We found different regimes of CCN activation and cloud formation for the month of May (shifting from aerosol-limited regime to transitional regime) and for June–July (transitional regime), which was primarily due to the variability of particle number concentrations in the accumulation mode.

Theoretical investigation of a potentially important formation pathway of organosulfate in atmospheric aqueous aerosols

Organic sulfate plays important roles in modulating properties of atmospheric aerosols. Recent studies showed that organic sulfate was likably interpreted as inorganic sulfate in field measurements using advanced instruments such as Aerosol Mass Spectrometer and the major contributor to organic sulfate was thought to be hydroxymethanesulfonate (HMS). This study proposed that besides HMS, its isomer hydroxymethyl sulfite (HMSi), which has not been identified in atmospheric aerosols, can emerge as the product of aqueous reactions between sulfur dioxide and formaldehyde. Results from quantum chemical modeling showed that formation of HMS and HMSi was several orders of magnitude faster than that of their corresponding conjugate acids, HMSA and HMHSi. In addition, water involvement can largely accelerate respectively the formation rate of HMS/HMSA and HMSi, but decelerate that of HMHSi, demonstrating the non-negligible role of water in the formation process. Furthermore, our kinetic model implemented with the calculated parameters indicates that HMSi/HMHSi but not HMS/HMSA can significantly alter the pH values of atmospheric aqueous aerosols and HMHSi is the most abundant species among HMS/HMSA and HMSi/HMHSi. Therefore, the newly-discovered pathway via HMSi/HMHSi formation should be of great concern and its kinetic parameters should be implemented in future models of atmospheric chemistry.

Impact of biogenic emissions of organic matter from a cool-temperate forest on aerosol optical properties

Abstract Terrestrial biogenic emissions of organic matter can affect the optical properties of atmospheric aerosols and thus impact the radiation budget. To investigate this, the chemical parameters of submicrometer water-soluble aerosols (WSA) collected on filters were compared to optical properties measured by a sky radiometer at a cool-temperate forest site in northern Japan. From June to December 2015, the WSA samples were collected within the forest canopy, while aerosol optical depth (AOD), single scattering albedo (SSA), absorption Angstrom exponent (AAE), and scattering Angstrom exponent (SAE) were retrieved above the canopy. The optical properties were compared with the filter-based chemical parameters only when the vertical transport of aerosol particles from the forest canopy to the air above it was significant. The result showed that the AOD and the mass concentrations of WSA exhibited similar and distinct seasonal variations with peaks in summer and autumn. In summer, sulfate accounted for 60% of the mass of WSA, which was linked to a high SSA (>0.95), low AAE (1.15 ± 0.84), and low SAE (1.25 ± 0.22). In contrast, water-soluble organic matter (WSOM) accounted for 70% of the mass of WSA in autumn. This large fraction of WSOM was associated with a decrease in SSA (0.90–0.95) and an increase in AAE (2.45 ± 0.91) and SAE (1.46 ± 0.15). The results suggest that in summer, aerosol particles with a greater size range corresponded to aerosol chemical compositions dominated by sulfate. In contrast, smaller particles with a strong light absorption at shorter wavelengths, were likely important in autumn and associated with a composition dominated by WSOM. The majority of WSOM in autumn has previously been associated with emissions of α-pinene from the forest floor and the subsequent formation of biogenic secondary organic aerosols (BSOA). This study indicates that α-pinene-derived SOAs, mostly originating from the forest floor, were associated with a summer to autumn decrease in SSA. This process can modulate the radiative effect on a regional scale.

Comparison of solid phase extraction methods for the measurement of humic-like substances (HULIS) in atmospheric particles

Humic-like substances (HULIS) constitute a significant fraction of the water-soluble organic compounds in the environment and influence many properties of atmospheric aerosols. In this study, three solid phase extraction (SPE) methods that involve the use of hydrophilic/lipophilic balanced (HLB) resin with pure methanol (HLB-M), HLB resin with 2% (v/v) ammonia/methanol (HLB-N), and Bond Elut PPL (Priority PolLutant) resin with methanol (PPL), were compared for the isolation of HULIS from atmospheric aerosols. The HLB-N and PPL methods efficiently recovered Suwannee River fulvic acid (SRFA) and were excellent for quantifying HULIS at low levels in aerosols. All three SPE methods were favorable for the elution of aromatic and strongly UV-absorbing compounds. However, the chemical structures and molecular compositions of the HULIS isolated by the three methods showed some differences. The HULISHLB-N and HULISPPL fractions contained higher concentrations of aliphatic and aromatic C–H groups than did the HULISHLB-M fraction, indicating that relative higher content of weak polar organic species in HULIS fractions isolated by the HLB-N and PPL methods than those isolated by the HLB-M method. Moreover, the HULISHLB-N and HULISPPL were both characterized by having lower relative abundance-weighted modified aromaticity index values and higher concentrations of S-containing compounds than the HULISHLB-M, as indicated by Fourier transform ion cyclotron resonance mass spectrometry. Some N-containing structures were identified only in the HULISHLB-N, suggesting that some of HULIS molecules were changed during the HLB-N treatment. Based on these comparisons of the three methods, we found that the PPL method serves equally good as compared to other two methods, and therefore, one can utilize PPL method also for HULIS isolation and characterization.

Aerosol Characteristics in the Near-Ground Layer of the Atmosphere of the City of Tomsk in Different Types of Aerosol Weather

Considering the wide range of variability of all aerosol characteristics (especially in the near-ground layer of the atmosphere near industrial centers), when creating a realistic empirical model of optical and microphysical characteristics, the optimal dividing of the total data array according to some multifactor signs is needed. In this paper, we analyze the main states of “dry” aerosol on the basis of the results of long-term regular measurements in the near-ground layer of the atmosphere near the city of Tomsk in 2000–2017. The following parameters were considered: aerosol number concentration and size distribution function, total and angular scattering coefficients, including the small-angle range 1.2° to 20°, mass concentration and size distribution of absorbing substances (equivalent black carbon), characteristics of the aerosol hygroscopic properties, and spectral aerosol extinction of radiation on an open long path in the wavelength range 0.45 to 3.9 µm. In our comprehensive study, we first proposed and developed an original approach (classification) to study the optical and microphysical properties of atmospheric aerosol of various physicochemical origins (background, smoke, smog, anthropogenic, etc.) based on dividing the entire data array into characteristic subarrays (types of aerosol weather), which differ from each other in a different combination of scattering and absorbing properties of particles. To divide the total data array into types of aerosol weather including “Background”, “Haze-S”, “Smog”, and “Smoke haze”, the values of the scattering coefficient of the dry aerosol matter σd(λ = 0.51 μm) = 100 Mm−1 and the ratio of the mass concentration of the absorbing substance to the mass concentration of submicron aerosol P = 0.05. The results showed that most of the seasonal average values of the aerosol parameters analyzed in the paper are statistically significantly different when comparing various characteristic types of scattering and absorbing atmospheric aerosol. The results of the research indicate that the application of the developed classification of types of aerosol weather for the analyzed optical and microphysical parameters of aerosol particles is quite effective and reasonable.

A new method to quantify mineral dust and other aerosol species from aircraft platforms using single-particle mass spectrometry

Abstract. Single-particle mass spectrometry (SPMS) instruments characterize the composition of individual aerosol particles in real time. Their fundamental ability to differentiate the externally mixed particle types that constitute the atmospheric aerosol population enables a unique perspective into sources and transformation. However, quantitative measurements by SPMS systems are inherently problematic. We introduce a new technique that combines collocated measurements of aerosol composition by SPMS and size-resolved absolute particle concentrations on aircraft platforms. Quantitative number, surface area, volume, and mass concentrations are derived for climate-relevant particle types such as mineral dust, sea salt, and biomass burning smoke. Additionally, relative ion signals are calibrated to derive mass concentrations of internally mixed sulfate and organic material that are distributed across multiple particle types. The NOAA Particle Analysis by Laser Mass Spectrometry (PALMS) instrument measures size-resolved aerosol chemical composition from aircraft. We describe the identification and quantification of nine major atmospheric particle classes, including sulfate–organic–nitrate mixtures, biomass burning, elemental carbon, sea salt, mineral dust, meteoric material, alkali salts, heavy fuel oil combustion, and a remainder class. Classes can be sub-divided as necessary based on chemical heterogeneity, accumulated secondary material during aging, or other atmospheric processing. Concentrations are derived for sizes that encompass the accumulation and coarse size modes. A statistical error analysis indicates that particle class concentrations can be determined within a few minutes for abundances above ∼10 ng m−3. Rare particle types require longer sampling times. We explore the instrumentation requirements and the limitations of the method for airborne measurements. Reducing the size resolution of the particle data increases time resolution with only a modest increase in uncertainty. The principal limiting factor to fast time response concentration measurements is statistically relevant sampling across the size range of interest, in particular, sizes D < 0.2 µm for accumulation-mode studies and D > 2 µm for coarse-mode analysis. Performance is compared to other airborne and ground-based composition measurements, and examples of atmospheric mineral dust concentrations are given. The wealth of information afforded by composition-resolved size distributions for all major aerosol types represents a new and powerful tool to characterize atmospheric aerosol properties in a quantitative fashion.