Measurements Of Aerosol Concentrations Research Articles

The Impact of a Severe Drought on Dust Lifting in California\u2019s Owens Lake Area

Mineral dust aerosols are responsible for some of the largest sources of uncertainties in our current understanding of climate change. Here we show that a severe drought is having a significant impact in one of largest sources of mineral dust aerosols of the U.S., the Owens Lake area in California’s southwest. Measurements of aerosol concentration (PM2.5 particle matter) in the Owens Lake salty playa show that the annual mean concentration of PM2.5 aerosol has been increasing steadily since the beginning of the current drought, with periods of high aerosol concentration increasing from 4 months in 2013 to 9 months in 2015. Interestingly, the PM2.5 aerosol concentration usually increases abruptly from less than ~0.05 mg/m3 to ~0.25 mg/m3. This occurs when saltation events break salt crusts produced by the efflorescence of brine in the salty playa. The brine is produced by either rainfall or runoff water. Based on this observation, we hypothesize that there is an upper limit of ~0.25 mg/m3 in the annual mean PM2.5 aerosols concentration in the Owens Lake basin that might limit the impact of mineral dust aerosols on climate. Indeed, the upper annual limit of ~0.25 mg/m3 has been nearly reached during the current drought.

Astronomical site survey report on dust measurement, wind profile, optical turbulence, and their correlation with seeing over IAO-Hanle

The present work discusses astronomical site survey reports on dust content, vertical distribution of atmospheric turbulence, precipitable water vapor (PWV), surface and upper-air data, and their effects on seeing over the Indian Astronomical Observatory (IAO) Hanle. Using Laser Particulate Counter, ambient dust measurements at various sizes (0.3 μm to 25 μm) were performed at various locations at the site during November 2015. Estimated volume concentration for the particle size at 0.5 μm was around 10,000 per cubic foot, which is equivalent to ten thousand class of clean room standard protocol. During the measurement, surface wind speed varied from 0-20 m s −1, while estimated aerosol optical depth (AOD) using Sky radiometer (Prede) varied from 0.02-0.04 at 500 nm, which indicates the site is fairly clean. The two independent measurements of dust content and aerosol concentrations at the site agreed well. The turbulence or wind gust at the site was studied with wind profiles at three different heights above the ground. The strength of the wind gust varies with time and altitude. Nocturnal temperature across seasons varied with a moderate at summer (6−8 ∘C) and lower in winter (4−5 ∘C). However, the contrast between the two is significantly small due to cold and extremely dry typical climatic conditions of the site. The present study also examined the effects of surface and upper-air data along with Planetary Boundary Layer (PBL) dynamics with seeing measurement over the site. Further, a comparative study of such observed parameters was conducted with other high altitude astronomical observatories across the globe.

Characteristics and source apportionment of black carbon aerosols over an urban site.

Aethalometer based source apportionment model using the measured aerosol absorption coefficients at different wavelengths is used to apportion the contribution of fossil fuel and wood burning sources to the total black carbon (BC) mass concentration. Temporal and seasonal variabilities in BC mass concentrations, equivalent BC from fossil fuel (BC f f ), and wood burning (BC w b ) are investigated over an urban location in western India during January 2014 to December 2015. BC, BC f f , and BC w b mass concentrations exhibit strong diurnal variation and are mainly influenced by atmospheric dynamics. BC f f was higher by a factor of 2-4 than BC w b and contributes maximum to BC mass throughout the day, confirming consistent anthropogenic activities. Diurnal contribution of BC f f and BC w b exhibits opposite variation due to differences in emission sources over Ahmedabad. Night time BC values are about a factor of 1.4 higher than day time BC values. The annual mean percentage contributions of day time and night time are 42 and 58 %, respectively. BC, BC f f , and BC w b mass concentrations exhibit large and significant variations during morning, afternoon, evening, and night time. During afternoon, mass concentration values are minimum throughout the year because of the fully evolved boundary layer and reduced anthropogenic activities. BC exhibits a strong seasonal variability with postmonsoon high (8.3 μg m -3) and monsoon low (1.9 μg m -3). Annual mean BC f f and BC w b contributions are 80 and 20 %, respectively, to total BC, which suggests that major contribution of BC in Ahmedabad comes from fossil fuel emissions. The results show that the study location is dominated by fossil fuel combustion as compared to the emissions from wood burning. The results obtained represent a regional value over an urban regime which can be used as inputs on source apportionment to model BC emissions in regional and global climate models.

Characterization of fine particles during the 2014 Asia-Pacific economic cooperation summit: Number concentration, size distribution and sources

To study the impacts of emission controls on aerosol physical and chemical properties, real-time measurements of size-resolved aerosol number concentration and chemical composition were conducted in urban Beijing during the 2014 Asia-Pacific Economic Cooperation (APEC) summit, in a period that a series of measures, for example shutting down or halting production from factories and power plants, and restricting the number of vehicles on the roads were implemented in Beijing and surrounding regions. Significantly, reductions in particle mass concentration (55% for PM2.5 and 48% for PM10) were observed during the APEC summit. A clear decrease in secondary inorganic aerosols (SIA), such as sulphate, nitrate and ammonium, was found during APEC, with the reduction ranged from 65.7 to 72.2% for PM1, in which sulphate showed the largest decrease compared with periods before APEC. As a comparison, organics showed a much smaller decrease of 44.3% for PM1 during APEC. These changes were mainly caused by large reductions in accumulation mode particles, which decreased by 36% compared with 19% for Aitken mode particles. The results from the positive matrix factorization (PMF) of particle number concentration indicate that regionally transported aerosols showed significant decreases (70%), similar to those of SIA during APEC, whereas primary factors from traffic and local combustion sources presented much smaller decreases, with the reduction ranged from 4 to 40%. The elevated contributions of these sources indicated the presence of strong local source emissions. The changes in particle chemical composition, size distribution and sources during the evolution of pollution episodes with and without emission controls are further illustrated. Our results highlight the importance of regional atmospheric transport in the formation of severe pollution episodes in Beijing, indicating that reducing the precursors of secondary aerosol over regional scales represent the key steps to reduce the urban particulate pollution. However, stricter emission controls on local source emissions are needed to further mitigate air pollution in Beijing.

Evidence of Sea-State Dependence of Aerosol Concentration in the Marine Atmospheric Boundary Layer

AbstractSea spray aerosols represent a large fraction of the aerosols present in the maritime environment. Despite evidence of the importance of surface wave– and wave breaking–related processes in coupling the ocean with the atmosphere, sea spray source generation functions are traditionally parameterized by the 10-m wind speed U10 alone. It is clear that unless the wind and wave field are fully developed, the source function will be a function of both wind and wave parameters. This study reports primarily on the aerosol component of an air–sea interaction experiment, the phased-resolved High-Resolution Air–Sea Interaction Experiment (HIRES), conducted off the coast of northern California in June 2010. Detailed measurements of aerosol number concentration in the marine atmospheric boundary layer (MABL) at altitudes ranging from as low as 30 m up to 800 m above mean sea level (MSL) over a broad range of environmental conditions (significant wave height Hs of 2 to 4.5 m and U10 from 10 to 18 m s−1) collected from an instrumented research aircraft are presented. Aerosol number densities and volume are computed over a range of particle diameters from 0.1 to 200 μm, while the sea surface conditions, including Hs, moments of the breaker length distribution Λ(c), and wave breaking dissipation, were measured by a suite of electro-optical sensors that included the NASA Airborne Topographic Mapper (ATM). The sea-state dependence of the aerosol concentration in the MABL is evident, stressing the need to incorporate wave parameters in the spray source generation functions that are traditionally parameterized by surface winds alone.

Long-term observations of cloud condensation nuclei in the Amazon rain forest – Part 1: Aerosol size distribution, hygroscopicity, and new model parametrizations for CCN prediction

Abstract. Size-resolved long-term measurements of atmospheric aerosol and cloud condensation nuclei (CCN) concentrations and hygroscopicity were conducted at the remote Amazon Tall Tower Observatory (ATTO) in the central Amazon Basin over a 1-year period and full seasonal cycle (March 2014–February 2015). The measurements provide a climatology of CCN properties characteristic of a remote central Amazonian rain forest site.The CCN measurements were continuously cycled through 10 levels of supersaturation (S = 0.11 to 1.10 %) and span the aerosol particle size range from 20 to 245 nm. The mean critical diameters of CCN activation range from 43 nm at S = 1.10 % to 172 nm at S = 0.11 %. The particle hygroscopicity exhibits a pronounced size dependence with lower values for the Aitken mode (κAit = 0.14 ± 0.03), higher values for the accumulation mode (κAcc = 0.22 ± 0.05), and an overall mean value of κmean = 0.17 ± 0.06, consistent with high fractions of organic aerosol.The hygroscopicity parameter, κ, exhibits remarkably little temporal variability: no pronounced diurnal cycles, only weak seasonal trends, and few short-term variations during long-range transport events. In contrast, the CCN number concentrations exhibit a pronounced seasonal cycle, tracking the pollution-related seasonality in total aerosol concentration. We find that the variability in the CCN concentrations in the central Amazon is mostly driven by aerosol particle number concentration and size distribution, while variations in aerosol hygroscopicity and chemical composition matter only during a few episodes.For modeling purposes, we compare different approaches of predicting CCN number concentration and present a novel parametrization, which allows accurate CCN predictions based on a small set of input data.

Six years of surface remote sensing of stratiform warm clouds in marine and continental air over Mace Head, Ireland

AbstractA total of 118 stratiform water clouds were observed by ground‐based remote sensing instruments at the Mace Head Atmospheric Research Station on the west coast of Ireland from 2009 to 2015. Microphysical and optical characteristics of these clouds were studied as well as the impact of aerosols on these properties. Microphysical and optical cloud properties were derived using the algorithm SYRSOC (SYnergistic Remote Sensing Of Clouds). Ground‐based in situ measurements of aerosol concentrations and the transport path of air masses at cloud level were investigated as well. The cloud properties were studied in dependence of the prevailing air mass at cloud level and season. We found higher cloud droplet number concentrations (CDNC) and smaller effective radii (reff) with greater pollution. Median CDNC ranged from 60 cm−3 in marine air masses to 160 cm−3 in continental air. Median reff ranged from 8 μm in polluted conditions to 10 μm in marine air. Effective droplet size distributions were broader in marine than in continental cases. Cloud optical thickness (COT) and albedo were lower in cleaner air masses and higher in more polluted conditions, with medians ranging from 2.1 to 4.9 and 0.22 to 0.39, respectively. However, calculation of COT and albedo was strongly affected by liquid water path (LWP) and departure from adiabatic conditions. A comparison of SYRSOC results with MODIS (Moderate‐Resolution Imaging Spectroradiometer) observations showed large differences for LWP and COT but good agreement for reff with a linear fit with slope near 1 and offset of −1 μm.

Deriving brown carbon from multiwavelength absorption measurements: method and application to AERONET and Aethalometer observations

Abstract. The radiative impact of organic aerosols (OA) is a large source of uncertainty in estimating the global direct radiative effect (DRE) of aerosols. This radiative impact includes not only light scattering but also light absorption from a subclass of OA referred to as brown carbon (BrC). However, the absorption properties of BrC are poorly understood, leading to large uncertainties in modeling studies. To obtain observational constraints from measurements, a simple absorption Ångström exponent (AAE) method is often used to separate the contribution of BrC absorption from that of black carbon (BC). However, this attribution method is based on assumptions regarding the spectral dependence of BC that are often violated in the ambient atmosphere. Here we develop a new AAE method which improves upon previous approaches by using the information from the wavelength-dependent measurements themselves and by allowing for an atmospherically relevant range of BC properties, rather than fixing these at a single assumed value. We note that constraints on BC optical properties and mixing state would help further improve this method. We apply this method to multiwavelength absorption aerosol optical depth (AAOD) measurements at AERONET sites worldwide and surface aerosol absorption measurements at multiple ambient sites. We estimate that BrC globally contributes up to 40 % of the seasonally averaged absorption at 440 nm. We find that the mass absorption coefficient of OA (OA-MAC) is positively correlated with the BC ∕ OA mass ratio. Based on the variability in BC properties and BC ∕ OA emission ratio, we estimate a range of 0.05–1.5 m2 g−1 for OA-MAC at 440 nm. Using the combination of AERONET and OMI UV absorption observations we estimate that the AAE388∕440 nm for BrC is generally ∼ 4 worldwide, with a smaller value in Europe (< 2). Our analyses of observations at two surface sites (Cape Cod, to the southeast of Boston, and the GoAmazon2014/5 T3 site, to the west of Manaus, Brazil) reveal no significant relationship between BrC absorptivity and photochemical aging in urban-influenced conditions. However, the absorption of BrC measured during the biomass burning season near Manaus is found to decrease with photochemical aging with a lifetime of ∼ 1 day. This lifetime is comparable to previous observations within a biomass burning plume but much slower than estimated from laboratory studies. Given the large uncertainties associated with AERONET retrievals of AAOD, the most challenging aspect of our analysis is that an accurate, globally distributed, multiple-wavelength aerosol absorption measurement dataset is unavailable at present. Thus, achieving a better understanding of the properties, evolution, and impacts of global BrC will rely on the future deployment of accurate multiple-wavelength absorption measurements to which AAE methods, such as the approach developed here, can be applied.

In situ and space-based observations of the Kelud volcanic plume: The persistence of ash in the lower stratosphere.

Volcanic eruptions are important causes of natural variability in the climate system at all time scales. Assessments of the climate impact of volcanic eruptions by climate models almost universally assume that sulfate aerosol is the only radiatively active volcanic material. We report satellite observations from the Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) on board the Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite after the eruption of Mount Kelud (Indonesia) on 13 February 2014 of volcanic materials in the lower stratosphere. Using these observations along with in situ measurements with the Compact Optical Backscatter AerosoL Detector (COBALD) backscatter sondes and optical particle counters (OPCs) made during a balloon field campaign in northern Australia, we find that fine ash particles with a radius below 0.3 µm likely represented between 20 and 28% of the total volcanic cloud aerosol optical depth 3 months after the eruption. A separation of 1.5–2 km between the ash and sulfate plumes is observed in the CALIOP extinction profiles as well as in the aerosol number concentration measurements of the OPC after 3 months. The settling velocity of fine ash with a radius of 0.3 µm in the tropical lower stratosphere is reduced by 50% due to the upward motion of the Brewer‐Dobson circulation resulting a doubling of its lifetime. Three months after the eruption, we find a mean tropical clear‐sky radiative forcing at the top of the atmosphere from the Kelud plume near −0.08 W/m2 after including the presence of ash; a value ~20% higher than if sulfate alone is considered. Thus, surface cooling following volcanic eruptions could be affected by the persistence of ash and should be considered in climate simulations.

Aerosol measurements during COPE: composition, size, and sources of CCN and INPs at the interface between marine and terrestrial influences

Abstract. Heavy rainfall from convective clouds can lead to devastating flash flooding, and observations of aerosols and clouds are required to improve cloud parameterisations used in precipitation forecasts. We present measurements of boundary layer aerosol concentration, size, and composition from a series of research flights performed over the southwest peninsula of the UK during the COnvective Precipitation Experiment (COPE) of summer 2013. We place emphasis on periods of southwesterly winds, which locally are most conducive to convective cloud formation, when marine air from the Atlantic reached the peninsula. Accumulation-mode aerosol mass loadings were typically 2–3 µg m−3 (corrected to standard cubic metres at 1013.25 hPa and 273.15 K), the majority of which was sulfuric acid over the sea, or ammonium sulfate inland, as terrestrial ammonia sources neutralised the aerosol. The cloud condensation nuclei (CCN) concentrations in these conditions were ∼ 150–280 cm−3 at 0.1 % and 400–500 cm−3 at 0.9 % supersaturation (SST), which are in good agreement with previous Atlantic measurements, and the cloud drop concentrations at cloud base ranged from 100 to 500 cm−3. The concentration of CCN at 0.1 % SST was well correlated with non-sea-salt sulfate, meaning marine sulfate formation was likely the main source of CCN. Marine organic aerosol (OA) had a similar mass spectrum to previous measurements of sea spray OA and was poorly correlated with CCN. In one case study that was significantly different to the rest, polluted anthropogenic emissions from the southern and central UK advected to the peninsula, with significant enhancements of OA, ammonium nitrate and sulfate, and black carbon. The CCN concentrations here were around 6 times higher than in the clean cases, and the cloud drop number concentrations were 3–4 times higher. Sources of ice-nucleating particles (INPs) were assessed by comparing different parameterisations used to predict INP concentrations, using measured aerosol concentrations as input. The parameterisations based on total aerosol produced INP concentrations that agreed within an order of magnitude with measured first ice concentrations at cloud temperatures as low as −12 °C. Composition-specific parameterisations for mineral dust, fluorescent particles, and sea spray OA were 3–4 orders of magnitude lower than the measured first ice concentrations, meaning a source of INPs was present that was not characterised by our measurements and/or one or more of the composition-specific parameterisations greatly underestimated INPs in this environment.

Intercomparison of aerosol extinction profiles retrieved from MAX-DOAS measurements

Abstract. A first direct intercomparison of aerosol vertical profiles from Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations, performed during the Cabauw Intercomparison Campaign of Nitrogen Dioxide measuring Instruments (CINDI) in summer 2009, is presented. Five out of 14 participants of the CINDI campaign reported aerosol extinction profiles and aerosol optical thickness (AOT) as deduced from observations of differential slant column densities of the oxygen collision complex (O4) at different elevation angles. Aerosol extinction vertical profiles and AOT are compared to backscatter profiles from a ceilometer instrument and to sun photometer measurements, respectively. Furthermore, the near-surface aerosol extinction coefficient is compared to in situ measurements of a humidity-controlled nephelometer and dry aerosol absorption measurements. The participants of this intercomparison exercise use different approaches for the retrieval of aerosol information, including the retrieval of the full vertical profile using optimal estimation and a parametrised approach with a prescribed profile shape. Despite these large conceptual differences, and also differences in the wavelength of the observed O4 absorption band, good agreement in terms of the vertical structure of aerosols within the boundary layer is achieved between the aerosol extinction profiles retrieved by the different groups and the backscatter profiles observed by the ceilometer instrument. AOTs from MAX-DOAS and sun photometer show a good correlation (R>0.8), but all participants systematically underestimate the AOT. Substantial differences between the near-surface aerosol extinction from MAX-DOAS and from the humidified nephelometer remain largely unresolved.

Impact of Marine-atmospheric Process on Aerosol Number Size Distribution in the South China Sea

The shipboard measurements of aerosol number concentration from August 28th to October 13th, 2012 were conducted to analyze the characteristics of temporal-spatial distribution and number size distribution of marine aerosol in the South China Sea. The impact of meteorological condition on the marine aerosol was also analyzed in this paper. The result showed that the temporal-spatial distribution and number size distribution of marine aerosol were influenced by the backward trajectory of the air masses and the time they spent over the sea, and the meteorological conditions in the local sea area such as wind speed, wind direction, temperature, relative humidity and cloud cover. In terms of temporal-spatial distribution of marine aerosol in the South China Sea, the aerosol in the sea areas under the influence of continental air mass concentration showed much higher concentration than that in the clean maritime air mass (2300 cm-3 vs. 1200 cm-3). During the ship observation, three kinds of number size distribution of marine aerosol were found and classified:polluted type, marine type 1 and marine type 2 (clean). All the distributions had a similar sub-micron mode and a similar coarse mode. The marine type 2 (clean) had the same distribution shape as polluted type except that the value of concentration was much lower. The sub-micron peak of marine type 1 appeared near 0.08 μm and its concentration was significantly higher than that of marine type 2 (clean). Non-precipitating clouds as well as abundant moisture contributed to the growth of ultrafine particles to the size of accumulation mode aerosol (0.05-0.12 μm). Number concentration of particles in this range showed weak positive correlation with wind speed since wind can enhance the efficiency of sea-air exchange and accelerate the release of gas precursors of sulfate aerosol to the atmosphere. The concentration of coarse particles ranging from 0.5-6 μm in diameter strongly depended on the wind speed, and the correlation coefficient reached a value of 0.7.

Black carbon and wavelength-dependent aerosol absorption in the North China Plain based on two-year aethalometer measurements

Light-absorbing components of atmospheric aerosols have gained particular attention in recent years due to their climatic and environmental effects. Based on two-year measurements of aerosol absorption at seven wavelengths, aerosol absorption properties and black carbon (BC) were investigated in the North China Plain (NCP), one of the most densely populated and polluted regions in the world. Aerosol absorption was stronger in fall and the heating season (from November to March) than in spring and summer at all seven wavelengths. Similar spectral dependence of aerosol absorption was observed in non-heating seasons despite substantially strong absorption in fall. With an average absorption Angström exponent (α) of 1.36 in non-heating seasons, freshly emitted BC from local fossil fuel burning was thought to be the major component of light-absorbing aerosols. In the heating season, strong ultraviolet absorption led to an average α of 1.81, clearly indicating the importance of non-BC light-absorbing components, which were possibly from coal burning for domestic heating and aging processes on a regional scale. Diurnally, the variation of BC mass concentrations experienced a double-peak pattern with a higher level at night throughout the year. However, the diurnal cycle of α in the heating season was distinctly different from that in non-heating seasons. α peaked in the late afternoon in non-heating seasons with concomitantly observed low valley in BC mass concentrations. In contrast, α peaked around the midnight in the heating season and lowered down during the daytime. The relationship of aerosol absorption and winds in non-heating seasons also differed from that in the heating season. BC mass concentrations declined while α increased with increasing wind speed in non-heating seasons, which suggested elevated non-BC light absorbers in transported aged aerosols. No apparent dependence of α on wind speed was found in the heating season, probably due to well mixed regional pollution. Pollution episodes were mostly encountered under low winds and had a low level of α, implying aerosol absorption should be largely attributed to freshly emitted BC from local sources under such conditions. Extensive field campaigns and long-term chemical and optical measurements of light-absorbing aerosols are needed in the future to further advance our understanding on optical properties of light-absorbing aerosols and their radiative forcing in this region.

Remote and in situ measurements of aerosol concentration in the Arctic troposphere from the Yak-42D “Roshydromet” research aircraft

The results are presented of measurements of aerosol content at different heights in the Arctic troposphere in the area of Naryan-Mar city and the Yamal Peninsula on June 24, 2014 using in situ and remote instruments installed on the Yak-42D "Roshydromet" research aircraft. The maximum aerosol content was detected in the layer up to 3000 m, and the aerosol concentration in the troposphere over the Yamal Peninsula is higher than that in the area of Naryan-Mar by 100 times. The in situ aircraft instrument measured the number concentration of black carbon particles in the tropospheric aerosol. To identify the sources of aerosol in the Arctic troposphere during airborne measurements the air mass trajectory analysis was performed. Simulations were conducted using the TRACAO trajectory model and FLEXPART particle dispersion model. The possible contribution of long-range and local transport of industrial pollutants to the Arctic troposphere was analyzed. The air mass transport was simulated using the trajectory model. Model computations of aerosol concentration in the troposphere using the satellite data on the gas flaring incite that the high content of black carbon in the lower troposphere over the Yamal Peninsula was caused by its transfer from the oil-producing areas located on the adjoining territory of Russia. The contribution of long-range transport of pollutants from industrial enterprises in Western Europe to the Arctic area under study was insignificant in the period under consideration.

Relationship of ground-level aerosol concentration and atmospheric electric field at three observation sites in the Arctic, Antarctic and Europe

Aerosol number concentrations in the particle size range from ~10nm to 1μm and vertical electric field strength in the surface layer was measured between September 2012 and December 2013 at three observation sites: mid-latitude station Swider, Poland, and, for the first time, in Hornsund in the Arctic, Spitsbergen, and the Antarctic Arctowski station in the South Shetland Islands. The measurements of aerosol concentrations have been performed simultaneously with measurements of the electric field with the aim to assess the local effect of aerosol on the electric field Ez near the ground at the three stations which at present form a network of atmospheric electricity observatories. Measurements have been made regardless of weather conditions at Swider and Arctowski station and mostly on fair-weather days at Hornsund station.The monthly mean particle number concentrations varied between 580 and 2100particlescm−3 at Arctowski, between 90 and 1270particlescm−3 in Hornsund, and between 6700 and 14,000particlescm−3 in the middle latitude station Swider. Average diurnal variations of the ground-level electric field Ez and particle number concentrations in fair-weather conditions were independent of each other for Arctowski and Hornsund stations. At Swider station the diurnal variation is usually characterized by an increase of aerosol concentration in the evening which results in the increased electric field. The assumption of neglecting the influence of varying aerosol concentration on the variation of the electric field in the polar regions, often adopted in studies, is confirmed here by the observations at Arctowski and Hornsund.The results of aerosol observations are also compared with modelled aerosol concentrations for global atmospheric electric circuit models.

Optical particle sensor based measurement and analysis of atmospheric aerosol number concentration of various sizes over a tropical region of Northern India

The measurement of atmospheric aerosol number concentration has been carried out at a remotely polluted site (Roorkee, 29o 52’ N, 77o 53’ E, 275 m above mean sea level) in northern India during pre monsoon period of 2009 at a height of 9 m above ground level. The aerosol number concentration having different sizes (0.3-0.5, 0.5-1.0, 1.0-2.0 and 2.0-5.0 μm) in pre monsoon summer season 0f 2009 has been analyzed, and the daily variation of aerosol number concentration has been related to selected meteorological parameters like as relative humidity, temperature, rainfall and wind speed. The measurements were made with an optical partical counter. The aerosol number concentration for upper size ranges (1.0-2.0 and 2.0-5.0 μm) is maximum in June and minimum in July. The aerosol number concentration in small size ranges (0.3-0.5 and 0.5-1.0 μm) decreases monotonically till the end of July.

Raman spectroscopic identification of size-selected airborne particles for quantitative exposure assessment

In this paper we present a method for the quantification of chemically distinguished airborne particulate matter, required for health risk assessment. Rather than simply detecting chemical compounds in a sample, we demonstrate an approach for the quantification of exposure to airborne particles and nanomaterials. In line with increasing concerns over the proliferation of engineered particles we consider detection of synthetically produced ZnO crystals. A multi-stage approach is presented whereby the particles are first aerodynamically size segregated from a lab-generated single component aerosol in an impaction sampler. These size fractionated samples are subsequently analysed by Raman spectroscopy. Imaging analysis is applied to Raman spatial maps to provide chemically specific quantification of airborne exposure against background which is critical for health risk evaluation of exposure to airborne particles. Here we present a first proof-of-concept study of the methodology utilising particles in the 2–4 μm aerodynamic diameter range to allow for validation of the approach by comparison to optical microscopy. The results show that the combination of these techniques provides independent size and chemical discrimination of particles. Thereby a method is provided to allow quantitative and chemically distinguished measurements of aerosol concentrations separated into exposure relevant size fractions.

Comparison of atmospheric particle concentration measurements using different optical detectors: Potentiality and limits for air quality applications

Optical detectors for atmospheric aerosol concentration measurements are often used in air quality applications given their potentialities for online measurements of air quality parameters at high temporal resolution. In this work the performances of different optical aerosol detectors used in air quality applications have been tested and compared for urban background aerosol conditions. Simultaneous measurements of aerosol number concentrations, size distributions and mass concentrations were taken in two different periods: November 2013 – February 2014 and May–June 2014 at an urban background site in Lecce (Southeastern Italy). Measurements were carried out using an OPC Grimm (mod. 1.109), an OPC FAI (Multichannel Monitor) and an optical photometer Mie pDR-1200. Good correlation, with determination coefficients R2 larger than 0.93 were found between particle number concentrations measured by the two OPCs both in accumulation (0.28–0.90μm for FAI and 0.29–0.90μm for Grimm) and coarse modes (1.10–10μm for FAI and 1.15–11.25μm for Grimm). Absolute counting for the accumulation fraction shows that Grimm OPC detects more particles (about 10%) than FAI OPC at concentration higher than 200,000particles/L in condition of high RH. This could be due to the changes of the optical properties of particles in high RH conditions visible even if the inlets of the two instruments are conditioned for lowering RH in sampled air. The differences in the absolute counting of the coarse fraction does not seems to be related to RH effects. The performances in evaluating mass concentrations PM10, and PM2.5 were evaluated comparing OPCs and pDR-1200 outputs with reference gravimetric and β-ray methods (that appeared to be essentially equivalent). Good agreement between Grimm OPC and SWAM is found both in PM10 and PM2.5 fractions while FAI OPC revealed greater discrepancy and scatter with respect to reference measurements. The performances of the pDR-1200 photometer were lower with respect to the OPCs with a larger influence of RH and optical properties of particles. The analysis of diurnal average trends in number and mass concentrations as well as the high temporal resolution responses of the instruments showed that optical detectors could be very useful to investigate atmospheric aerosol for air quality applications and to individuate and investigate specific pollution events. However, especially if they are used for evaluating mass concentrations (PM1, PM2.5 or PM10), it is necessary to take into account RH effects (even if the inlet are conditioned) and, possibly, use optical detectors together with reference gravimetric or β-ray methods to check their response in the effective operative conditions.

Measurement and analysis of black carbon aerosols over a tropical semi-arid station in Kadapa, India

This paper presents aerosol light absorption measurements using a seven channel Aethalometer (AE-42), recorded during September 2011–November 2012 over a tropical semi-arid site in Kadapa, India. The annual average black carbon (BC) mass concentration ([BC]) during the studied period was 2.20±0.78μgm−3 which is in agreement when compared to other sites of similar environment. Strong seasonal variation was observed with high values during winter (2.87±0.81μgm−3) and low in monsoon (1.30±0.31μgm−3) season, which could be attributed to regional synoptic meteorology and long range transport. The two peaks in diurnal variations of [BC] were observed during morning between 06:00 and 08:00h local time (LT) and in the evening around 19:00–21:00h LT, with a minimum peak in the afternoon (~16:00h LT) which is strongly correlated with the boundary layer dynamics, local and regional sources, and associated meteorology. The relationships between measured [BC] and the corresponding meteorological parameters for the studied region were also analysed. The estimated monthly mean spectral absorption coefficient values range from 0.56 to 1.15 with an average of 0.90, which suggests high BC/OC ratio and possible source of emission of aerosols is fossil fuel burning. Trajectory cluster analysis showed significant impact of long range transport of BC aerosols towards the observational site during the period of study.

A light-weight, high-sensitivity particle spectrometer for PM2.5 aerosol measurements

ABSTRACTA light-weight, low-cost optical particle spectrometer for measurements of aerosol number concentrations and size distributions has been designed, constructed, and demonstrated. The spectrometer is suitable for use on small, unmanned aerial vehicles (UAVs) and in balloon sondes. The spectrometer uses a 405 nm diode laser to count and size individual particles in the size range 140–3000 nm. A compact data system combines custom electronics with a single-board commercial computer. Power consumption is 7W at 9–15 V. 3D printing technology was used in the construction of the instrument to reduce cost, manufacturing complexity, and weight. The resulting Printed Optical Particle Spectrometer (POPS) instrument weighs about 800 g with an approximate materials cost of 2500 USD. Several POPS units have been constructed, tested in the laboratory, and deployed on UAVs. Here we present an overview of the instrument design and construction, laboratory validation data, and field engineering data for POPS.