Changes In Aerosol Size Distribution Research Articles

Changes in aerosol size distributions over the Indian Ocean during different meteorological conditions

Aerosol emissions in South Asia are large. The emitted aerosols can travel significant distances and, during the Asian southwest monsoon especially, are prone to modification through cloud processing and wet scavenging while being transported. The scale of emissions and transport means that the global climate impact of these aerosols are sensitive to modification en route, but the process-level understanding is still largely lacking. In this study, we analyse long-term aerosol data measured at an observatory established in Hanimaadhoo, Republic of Maldives, to investigate the long-term properties of aerosols over the Indian Ocean as well as to understand the effect of precipitation on the aerosol particle size distribution during long-range transport. The observatory location is ideal because it is a receptor site with little local influence, and, depending on the season, receives either polluted air masses coming from the Indian subcontinent or clean marine air masses from the Indian Ocean. We analysed the sub-micron particle number size distribution measured during the years 2004–2008, and 2014–2017, and this is the first inter-seasonal long-term study of the sub-micron aerosol features in the region. The aerosol origin and its relative exposure to wet scavenging during long-range transport were analysed using back-trajectory analysis from HYSPLIT. By comparing aerosol measurements to precipitation along its transport, this study shows that there is a substantial change in particle number size distributions and concentrations depending on the amount of rainfall during transport. During the southwest monsoon season, the aerosol size distribution was notably bi-modal and total particle concentrations clearly reduced in comparison with the prevailing aerosol size distribution during the northeast monsoon season. Precipitation during transport usually corresponded with a greater reduction in accumulation mode concentrations than for smaller sizes, and the shape of the median size distribution showed a clear dependence on the trajectory origin and route taken.

Chemical separation in a binary liquid aerosol by filtration using electrospun membranes

Binary liquid aerosols were filtered using electrospun fiber membranes for the purpose of demonstrating the feasibility of changing aerosol composition through size selection. The impacts of filtration on the particle size distribution and the overall composition of the aerosols were studied and correlated to the filter properties. The binary liquid aerosols comprised di(2-ethylhexyl) sebacate and di(2-ethylhexyl) phthalate, with median mobility diameters between 200 nm and 300 nm. Droplet size-resolved measurements of aerosol composition, performed using a combination of cascade impactor and gas chromatography-mass spectrometry (GC–MS), revealed size-dependent compositional variation. Electrospun membranes of polyacrylonitrile with four different fiber diameters, ranging from 300 nm to 1 μm, were tested. The membranes with small fiber diameters were more likely to have significant impact on both the size and composition of the aerosols. Electrospun membranes consisting of 300 nm diameter fibers altered the median particle diameter by as much as 4%, and the overall composition of the aerosols by as much as 30%. Membranes with large fiber diameters, on the other hand, exhibited negligible effects on the aerosol systems with regard to both aerosol size and composition. Electrospun cellulose acetate membranes of different thicknesses were also tested on a binary aerosol system with the same components. Thicker filters resulted in greater decrease in mean particle size and greater change of aerosol composition, up to 16%. The changes in aerosol size distribution and composition upon filtration were correlated through the droplet size-dependence of the aerosol composition.

Summer-autumn air pollution in León, Spain: changes in aerosol size distribution and expected effects on the respiratory tract

The temporal variation of aerosol size distribution in Leon, Spain, was analyzed with an optical spectrometer, in order to identify changes associated with the summer-autumn transition. For each hour and day of the week, we have studied the temporal variation of the particle number during the day. As the summer progresses, the total particle number increases from 1000 ± 600 in August to 1500 ± 1000 particles cm−3 in October, mainly due to more intense road traffic after the summer holidays and to the beginning of the new academic year in the study area in September. The particle number was higher on weekdays than on weekends in September and October. However, in August the values were similar, due to lower activity in the city, coinciding with the main holiday period. The aerosol size distributions were bimodal. In the fine mode, both the highest concentration (573 particles cm−3) and the lowest count median diameter (0.08 μm) were recorded in October. The contribution of particles from forest fires and Saharan dust intrusions had a negative impact on the air quality of the city during the summer. Considering the estimated respirable fraction in healthy adults (after the Standard ISO 7708:1995), on weekdays the highest values are obtained between 0600 and 1000 UTC (around 15 μg m−3) and in the afternoon, between 1700 and 2000 UTC (around 12 μg m−3), coinciding with the rush hour.

Aerosol, Ozone and Water Vapour Distributions Observed over Land and Sea Regions during INDOEX Field Phases

Extensive land- and ocean-based experiments involving active and passive remote sensing of aerosols and minor constituents have been conducted simultaneously over Pune and over the Indian Ocean and Arabian Sea during the INDian Ocean EXperiment (INDOEX) field phases with an aim to study the interface between the polluted continental air-mass and pristine marine air-mass, and the underlying circulat ion and Inter Tropical Convergence Zone (ITCZ) phenomena, which mixes the polluted air mass from Northern hemisphere with the pristine air mass from the Southern hemisphere. In this communicat ion, we report some important findings of the special observational programs which were carried out during the First Field Phase (FFP) i.e. fro m 17 February to 31 March 1998 and Intense Field Phase (IFP) i.e. fro m 1 January to 31 March 1999 of the INDOEX. These programs involve synchronous measurements of aerosol, ozone and precipitable water vapor using ground-based lidar, sunphotometer / spectroradiometer and ozone / water vapor monitor at the Indian Institute of Tropical Meteorology (IITM ), Pune, India, and aerosol characterization over the Indian Ocean and Arabian Sea utilizing a mult i-channel solar radio meter installed onboard Ocean Research Vessel (ORV) Sagar Kanya ship. Besides significant deviations between aerosol features over the land and oceanic regions, the lidar derived aerosol colu mn content (ACC) in the boundary layer, and radio meter derived height-integrated aerosol optical depth (AOD) show significant trend and characteristic changes in aerosol size distribution over land during both FFP and IFP. Moreover, the IFP measurements indicate higher aerosol ext inction (particularly in the initial period) as co mpared to those of FFP. On some experimental days, the land AODs appear to be of the magnitude similar to those of marine AODs observed close to the Indian subcontinent and adjoining South Asian regions. The variations in AOD over land also show an association with those observed over ocean, particularly near the coast. Besides an increasing trend in total colu mn ozone throughout the IFP, it exhib its a specific relat ionship with those observed in AOD and water vapor over land. Co mparison between the boundary layer and total column AODs reveals that the observed increasing trend in AOD is not confined to the boundary layer alone but extends to higher altitudes with significant contribution fro m the former to the latter.

Impact of Two-Way Aerosol–Cloud Interaction and Changes in Aerosol Size Distribution on Simulated Aerosol-Induced Deep Convective Cloud Sensitivity

AbstractRecent cloud-resolving model studies of single (isolated) deep convective clouds have shown contradicting results regarding the response of the deep convection to changes in the aerosol concentration. In the present study, a cloud-resolving model including explicit aerosol physics and chemistry is used to examine how the complexity of the aerosol model, the size of the aerosols, and the aerosol activation parameterization influence the aerosol-induced deep convective cloud sensitivity. Six sensitivity series are conducted. A significant difference in the aerosol-induced deep convective cloud sensitivity is found when using different complexities of the aerosol model and different aerosol activation parameterizations. In particular, graupel impaction scavenging of aerosols appears to be a crucial process because it efficiently may limit the number of cloud condensation nuclei (CCN) at a critical stage of cloud development and thereby dampen the convection. For the simulated case, a 100% increase in aerosol concentration results in a difference in average updraft between the various sensitivity series that is as large as the average updraft increase itself. The change in graupel and rain formation also differs significantly. The sign of the change in precipitation is not always directly proportional to the change in updraft velocity and several of the sensitivity series display a decrease of the rain amount with increasing updraft velocity. This result illustrates the need to account for changes in evaporation processes and subsequent cooling when assessing aerosol effects on deep convective strength. The model simulations also show that an increased number of aerosols in the Aitken mode (here defined by 23 ≤ d ≤ 100.0 nm) results in a larger impact on the convective strength compared to an increased number of aerosols in the accumulation mode (here defined by 100 ≤ d ≤ 900.0 nm). When accumulation mode aerosols are activated and grow at the beginning of the cloud cycle, the supersaturation near the cloud base is lowered, which to some extent limits further aerosol activation. The simulations indicate a need to better understand and represent the two-way interaction between aerosols and clouds when studying aerosol-induced deep convective cloud sensitivity.

Cloud condensation nucleus (CCN) behavior of organic aerosol particles generated by atomization of water and methanol solutions

Abstract. Cloud condensation nucleus (CCN) experiments were carried out for malonic acid, succinic acid, oxalacetic acid, DL-malic acid, glutaric acid, DL-glutamic acid monohydrate, and adipic acid, using both water and methanol as atomization solvents, at three operating supersaturations (0.11%, 0.21%, and 0.32%) in the Caltech three-column CCN instrument (CCNC3). Predictions of CCN behavior for five of these compounds were made using the Aerosol Diameter Dependent Equilibrium Model (ADDEM). The experiments presented here expose important considerations associated with the laboratory measurement of the CCN behavior of organic compounds. Choice of atomization solvent results in significant differences in CCN activation for some of the compounds studied, which could result from residual solvent, particle morphology differences, and chemical reactions between the particle and gas phases. Also, significant changes in aerosol size distribution occurred after classification in a differential mobility analyzer (DMA) for malonic acid and glutaric acid, preventing confident interpretation of experimental data for these two compounds. Filter analysis of adipic acid atomized from methanol solution indicates that gas-particle phase reactions may have taken place after atomization and before methanol was removed from the sample gas stream. Careful consideration of these experimental issues is necessary for successful design and interpretation of laboratory CCN measurements.

Is nucleation capable of explaining observed aerosol integral number increase during southerly transport over Scandinavia?

Using a pseudo-Lagrangian approach, changes in aerosol size distribution was investigated during southerly transport under clear sky conditions from Finnish Lapland to Hyytiälä. Seventy-nine individual transport cases were considered. The mean transport distance was 700 km and mean transport time 66 h. On average, a sevenfold increase in Aitken mode number concentration could be observed. An increase in number concentration was observed in virtually all the cases. Several of the studied cases were associated with indications of nucleation at the receptor site. Six of the cases were simulated in detail utilizing a box-model approach. Aerosol dynamics was evaluated using the University of Helsinki Multi-component Aerosol model. Particle formation was assumed to be controlled by a kinetic nucleation mechanism. Growth of particles was suggested to be controlled by, except water and ammonia, sulphuric acid, and some unknown species with saturation vapour pressure of 3 × 106 cm-3. This product was supposed to derive from terpene oxidation by hydroxyl radical, ozone, and nitrate radical.The investigation strongly suggests nucleation events occurring over large scales to be responsible for the observed number increase during transport under modelled conditions.Using a simplified two layer structure of the lowermost troposphere, we highlight the role of vertical exchange.Modelled growth rates were found to be in agreement with observational data, in the order of 1–2 nm h–1. In order to reproduce the observed growth rates, a molar yield of condensable products from terpene oxidation of 10% was required. Concentration of sulphuric acid and condensable organic vapours were on average 3 × 106 and 1.5 × 107 cm-3, respectively.

Size Distribution of Chromate Paint Aerosol Generated in a Bench-Scale Spray Booth

Spray painters are potentially exposed to aerosols containing hexavalent chromium [Cr(VI)] via inhalation of chromate-based paint sprays. Evaluating the particle size distribution of a paint spray aerosol, and the variables that may affect this distribution, is necessary to determine the site and degree of respiratory deposition and the damage that may result from inhaled Cr(VI)-containing paint particles. This study examined the effect of spray gun atomization pressure, aerosol generation source and aerosol aging on the size distribution of chromate-based paint overspray aerosols generated in a bench-scale paint spray booth. The study also determined the effect of particle bounce inside a Marple personal cascade impactor on measured size distributions of paint spray aerosols. Marple personal cascade impactors with a modified inlet were used for sample collection. The data indicated that paint particle bounce did not occur inside the cascade impactors sufficiently to affect size distribution when using uncoated stainless steel or PVC substrate sampling media. A decrease in paint aerosol mass median aerodynamic diameter (MMAD) from 8.2 to 7.0 mum was observed as gun atomization pressure increased from 6 to 10 psi. Overspray aerosols were sampled at two locations in the spray booth. A downstream sampling position simulated the exposure of a worker standing between the painted surface and exhaust, a situation encountered in booths with multiple workers. The measured mean MMAD was 7.2 mum. The distance between the painted surface and sampler was varied to sample oversprays of varying ages between 2.8 and 7.7 s. Age was not a significant factor for determining MMAD. Overspray was sampled at a 90 degrees position to simulate a worker standing in front of the surface being painted with air flowing to the worker's side, a common situation in field applications. The resulting overspray MMAD averaged 5.9 mum. Direct-spray aerosols were sampled at ages from 5.3 to 11.7 s. Overspray and direct-spray results indicated that most of the change in aerosol size distribution occurred between the time the paint aerosol impacted the painted surface and the time the overspray became 2.8 s old. The overall mean MMAD of overspray in the study was 6.4 mum and may have been underestimated due to sampling efficiency biases. If inhaled by a worker, the overspray aerosols evaluated in this study would mostly deposit in the head airways region of the respiratory tract. Paint overspray aerosols contained Cr primarily in the Cr(VI) state.

Photometer response determination based on aerosol physical characteristics.

Aerosol photometers often are calibrated against field measurements of total or respirable aerosol concentrations. However, the response of these instruments to a particular aerosol concentration level will change if there is a change in aerosol size distribution. To determine a predictable correction factor that relates photometer to gravimetric measurements of an aerosol, the authors performed an analysis of photometer response relative to particle size distribution, density, and refractive index. A series of trials was performed at different concentration levels using both Arizona road dust and ground corn dust. The correction factor was calculated from a knowledge of the instrument response pattern relative to particle size, as well as the ratios of actual dust density and refractive index relative to that of the dust used to calibrate the instruments. Results demonstrated that the calculated correction factors were within 10% of a correction factor predicted from the slope of a linear regression relating gravimetric measurements to the average of photometer readings taken during the sample period.

Daily changes in aerosol size distribution in a greenhouse

Daily changes in aerosol size distribution in a greenhouse

Vertical distribution of aerosol particles and CCN in clear air around the British Isles

We present vertical profiles of aerosol particles and cloud condensation nuclei (CCN) obtained during four flights around the British Isles under different synoptic situations and in different seasons. The calculated net downward radiative flux was reduced significantly by the presence of an aerosol layer close to the surface, especially for the two very polluted days. The heating rates in the aerosol layer increased by between a factor of 2 and more than an order of magnitude. Particle and CCN concentrations after air mass passage over the U.K. increased by about a factor of 2, the changes in the spectra being due to increases in the concentration of particles smaller than 0.2 μm in radius and to decreases in the concentration of large particles (5–11)μm). The changes in aerosol size distributions after air mass passage over land resulted in changes in microphysical and radiative characteristics of the clouds that developed. There is evidence that non-hygroscopic aerosol particles account for up to 50% of the aerosol particle number concentration during two heavily polluted flights.

Measurement of the change in aerosol size distribution with bacterial growth in a pilot scale fermentor

A number of industrial processes require the addition of materials to the fermentation broth that are hazardous to health and environment. Agitation of broths inoculated with microorganisms can potentially release aerosols large enough to carry the microorganisms. The influence of agitation, air flow, and bacterial growth on aerosol size distribution, air flow, and bacterial growth on aerosol size distribution was investigated in an industrial pilot scale fermentor. A decrease in particle concentration was observed with increase in bacterial growth; this change was more pronounced in the size range above 2 microm. The aerosol size distribution was found to be practically independent of air flow rate and agitation rate for sizes less than 2 microm. However, for particles larger than 2 microm, the concentration was found to increase with an increase in air flow rate and agitation rate.

Variation of atmospheric optical depth for remote sensing radiance calculations

An analysis of the radiative transfer processes in the atmosphere suggests that the ratio between the diffuse radiance flux and the directly transmitted flux may be a useful parameter for investigating the variation of atmospheric optical depth. The radiative parameter is derived for an observer at the top of the atmosphere in the position of a satellite. One of the important variables required in the computations of the radiative parameter is the aerosol phase function which can be satisfactorily fitted by the two-term Henyey-Greenstein function. When the surface reflectance equals zero, representing the atmospheric radiance alone without any influence from an oceanic surface, the study shows that the variation of the optical depth is associated with the changing of aerosol size distribution. The optical depth increases with the presence of large aerosol particles. The results indicate that inhomogeneities in aerosol optical properties, such as the variation of the scattering phase function due to the changes in aerosol size distribution, can affect the magnitude of the optical depth.

Mathematical model for multicomponent aerosol formation and growth in plumes

Description of the evolution of the size and chemical composition of aerosols in plumes is fundamental to the ability to predict visibility impairment. Previously it has only been possible to predict changes in aerosol size distributions in plumes. In this work the first model for predicting both size and chemical composition evolution of plume aerosols is presented. Coagulation, homogeneous particle formation, heterogeneous condensation and particulate phase chemical equilibria and kinetics are explicitly included. The model is based on a sectional representation of the size-composition spectrum and computation is easy to implement. This model holds promise to be a standard component of all plume visibility calculations that require plume aerosol size and composition information.