Optical Properties Of Aerosol Particles Research Articles

Optical Properties of Aerosol Particles in the Atmospheric Boundary Layer over the Northwestern Pacific: High Refractive Index for Coarse Particles in Pristine Air

Optical Properties of Aerosol Particles in the Atmospheric Boundary Layer over the Northwestern Pacific: High Refractive Index for Coarse Particles in Pristine Air

Aerosol particle properties at a remote tropical rainforest in Borneo

This paper aims to investigate aerosol particle properties and their seasonal variabilities at a remote tropical forest site. It also attempts to study the relationship between aerosol particles and dynamic atmospheric processes that modulate aerosol variability. Mass concentrations for particles smaller than 10 μm aerodynamic diameter (PM10) and optical aerosol particle properties were measured at Danum Valley tropical rainforest in Borneo Island. The particle mass concentrations were measured using a Tapered Element Oscillating Microbalance (TEOM). Measurements of aerosol particle optical properties, i.e., the particle light absorption and scattering coefficients, were conducted using a Multi-Angle Absorption Photometer (MAAP) and nephelometer, respectively. The single scattering albedo (SSA) and scattering Angstrom exponent (SAE) were calculated from the aerosol scattering and absorption coefficients. The results showed that the daily average of PM10 mass concentrations was 12.3 μgm−3, while the particle light absorption coefficients at wavelength 637 nm and scattering coefficients at wavelength 525 nm were reported as 2.7 Mm−1 and 21.7 Mm−1, respectively. The daily average SSA and SAE recorded were 0.89 and 1.44, respectively. The SSA showed no seasonal variations while higher SAE was observed during the dry season due to the influence of biomass burning originating from the southern region of Borneo. The wavelet analysis showed strong intra-seasonal cycles (12–20 and 32–64 days) which suggest the influence of Quasi-BiWeekly (QBW) oscillation and Madden-Julian Oscillation (MJO) on the aerosol variability over the tropics. The analysis also showed seasonal and annual variability bands, generally associated with the dry and wet seasons over the region.

Optical properties of aerosol particles in the atmospheric boundary layer in regions with and without sea ice

The optical properties of aerosol particles must be clearly understood to reduce uncertainty in the prediction of the global climate change. Simultaneous measurements of scattering and absorption coefficients of aerosol particles were conducted in the atmospheric boundary layer over the western North Pacific and the Southern Ocean. For the scattering coefficient, total scattering and backscattering coefficients were measured at three different wavelengths. Over the western North Pacific, significant differences in the Ångström exponent and absorption coefficient were found between polluted and pristine air masses. Over the parts of the Southern Ocean free of sea ice, the Ångström exponent and the ratio of the back-to total-scattering coefficients were uniform. However, over the sea-ice regions, the scattering coefficients were an order of magnitude lower, and the Ångström exponent an order of magnitude higher, than over the parts of the ocean free of sea ice. These differences appear to be due to the fact that the emission of aerosol precursors and sea salt particles is suppressed by sea ice. This study represents the difference in aerosol optical properties as a function of source region and sea condition. These results will contribute to improving the accuracy of estimates of the direct radiative forcing effects due to aerosol particles.

Aircraft vertical profiles during summertime regional and Saharan dust scenarios over the north-western Mediterranean basin: aerosol optical and physical properties

Abstract. Accurate measurements of the horizontal and vertical distribution of atmospheric aerosol particle optical properties are key for a better understanding of their impact on the climate. Here we present the results of a measurement campaign based on instrumented flights over north-eastern Spain. We measured vertical profiles of size-segregated atmospheric particulate matter (PM) mass concentrations and multi-wavelength scattering and absorption coefficients in the western Mediterranean basin (WMB). The campaign took place during typical summer conditions, characterized by the development of a vertical multi-layer structure, under both summer regional pollution episodes (REGs) and Saharan dust events (SDEs). REG patterns in the region form under high insolation and scarce precipitation in summer, favouring layering of highly aged fine-PM strata in the lower few kma.s.l. The REG scenario prevailed during the entire measurement campaign. Additionally, African dust outbreaks and plumes from northern African wildfires influenced the study area. The vertical profiles of climate-relevant intensive optical parameters such as single-scattering albedo (SSA); the asymmetry parameter (g); scattering, absorption and SSA Ångström exponents (SAE, AAE and SSAAE); and PM mass scattering and absorption cross sections (MSC and MAC) were derived from the measurements. Moreover, we compared the aircraft measurements with those performed at two GAW–ACTRIS (Global Atmosphere Watch–Aerosol, Clouds and Trace Gases) surface measurement stations located in north-eastern Spain, namely Montseny (MSY; regional background) and Montsec d'Ares (MSA; remote site). Airborne in situ measurements and ceilometer ground-based remote measurements identified aerosol air masses at altitudes up to more than 3.5 kma.s.l. The vertical profiles of the optical properties markedly changed according to the prevailing atmospheric scenarios. During SDE the SAE was low along the profiles, reaching values < 1.0 in the dust layers. Correspondingly, SSAAE was negative, and AAE reached values up to 2.0–2.5, as a consequence of the UV absorption increased by the presence of the coarse dust particles. During REG, the SAE increased to > 2.0, and the asymmetry parameter g was rather low (0.5–0.6) due to the prevalence of fine PM, which was characterized by an AAE close to 1.0, suggesting a fossil fuel combustion origin. During REG, some of the layers featured larger AAE (> 1.5), relatively low SSA at 525 nm (< 0.85) and high MSC (> 9 m2 g−1) and were associated with the influence of PM from wildfires. Overall, the SSA and MSC near the ground ranged around 0.85 and 3 m2 g−1, respectively, and increased at higher altitudes, reaching values above 0.95 and up to 9 m2 g−1. The PM, MSC and MAC were on average larger during REG compared to SDE due to the larger scattering and absorption efficiency of fine PM compared with dust. The SSA and MSC had quite similar vertical profiles and often both increased with height indicating the progressive shift toward PM with a larger scattering efficiency with altitude. This study contributes to our understanding of regional-aerosol vertical distribution and optical properties in the WMB, and the results will be useful for improving future climate projections and remote sensing or satellite retrieval algorithms.

From a polar to a marine environment: has the changing Arctic led to a shift in aerosol light scattering properties?

Abstract. The study of long-term trends in aerosol optical properties is an important task to understand the underlying aerosol processes influencing the change of climate. The Arctic, as the place where climate change manifests most, is an especially sensitive region of the world. Within this work, we use a unique long-term data record of key aerosol optical properties from the Zeppelin Observatory, Svalbard, to ask the question of whether the environmental changes of the last 2 decades in the Arctic are reflected in the observations. We perform a trend analysis of the measured particle light scattering and backscattering coefficients and the derived scattering Ångström exponent and hemispheric backscattering fraction. In contrast to previous studies, the effect of in-cloud scavenging and of potential sampling losses at the site are taken explicitly into account in the trend analysis. The analysis is combined with a back trajectory analysis and satellite-derived sea ice data to support the interpretation of the observed trends. We find that the optical properties of aerosol particles have undergone clear and significant changes in the past 2 decades. The scattering Ångström exponent exhibits statistically significant decreasing of between −4.9 % yr−1 and −6.5 % yr−1 (using wavelengths of λ=450 and 550 nm), while the particle light scattering coefficient exhibits statistically significant increasing trends of between 2.6 % yr−1 and 2.9 % yr−1 (at a wavelength of λ=550 nm). The magnitudes of the trends vary depending on the season. These trends indicate a shift to an aerosol dominated more by coarse-mode particles, most likely the result of increases in the relative amount of sea spray aerosol. We show that changes in air mass circulation patterns, specifically an increase in air masses from the south-west, are responsible for the shift in aerosol optical properties, while the decrease of Arctic sea ice in the last 2 decades only had a marginal influence on the observed trends.

Кутові характеристики розсіювання сонячного світла земною атмосферою, спостережувані приладом «ScanPol» проєкту «АEROSOL-UА»

Angular characteristics of solar light scattering in the Earth’s atmosphere and parameters of the atmosphere volume and the surface part observed by the ScanPol instrument of the “Aerosol-UA” project are estimated in order to determine properties of aerosol particles from a satellite orbit. Estimations were obtained for the scattering angles ranges in the lower troposphere which can be observed by the ScanPol instrument from the polar sun-synchronous orbit with altitude 705 km and inclination 98.1° crossing the ascending knot on the equator at 21h 30m, 22h 30m, and 23h 30m of local mean solar time. The estimations of the scattering angles were obtained at each of the orbit realizations for sites on the Earth’s surface, were the zenith angle of the Sun is 80°, 50°, and minimal one for each of the orbit realizations. The calculations were performed for the dates of 2020 close to the summer solstice, the autumnal equinox, and the winter solstice (namely 21 June, 21 September, and 21 December, respectively). The scattering angles range was computed for the range of the ScanPol scanning angles equal to 110° along the sub-satellite trace. The range of scattering angles is maximal at the considered here maximal zenith angle of the Sun equal to 80°, which occurs in the polar latitudes of the northern hemisphere during the period between the spring and the autumnal equinoxes and in the middle latitudes during the rest of a year. The maximal range of scattering angles is approximately 51.1°...149.5° close to the summer solstice for the satellite orbit with local time of crossing the ascending knot (TBB) equal to 21h 30m and 41.9°...172.9° for the orbit with ТВВ = 23h 30m. The minimal range of scattering angles occurs at minimal zenith angles of the Sun close to the winter solstice and takes on the values approximately 103.2°...142.8° and 108.2°...170.4° at mentioned ТВВ, respectively. For the rest of the zenith angles of the Sun, the range of scattering angles takes on the intermediate values. The range of scattering angles decreased mainly at the cost of small scattering angles. In summary, the range of observed scattering angles is maximal for the orbit with local time close to the noon, to be precise at TBB between 22h 30m and 24h 00m for the orbit with inclination assumed here. Comparison of the ranges of scattering angles observed by the ScanPol instrument and data of simulations showed that measurements by ScanPol from the considered orbit allow us to retrieve microphysical and optical properties of aerosol particles. Linear size of the scene observed by instrument along the sub-satellite trace increases during the scanning process from approximately 6 km at nadir to almost 60 km at maximal scattering angle equal to 60°, and simultaneously the longitude of the observed scene decreases by 1.55° that corresponds to linear shift along the parallel from DS »172 km on the equator to DS » 24.5 km on the latitude 82°. That is why data measured by the ScanPol can be used after mesoscale averaging.

Biomass burning and urban emission impacts in the Andes Cordillera region based on in situ measurements from the Chacaltaya observatory, Bolivia (5240 m a.s.l.)

Abstract. This study documents and analyses a 4-year continuous record of aerosol optical properties measured at the Global Atmosphere Watch (GAW) station of Chacaltaya (CHC; 5240 m a.s.l.), in Bolivia. Records of particle light scattering and particle light absorption coefficients are used to investigate how the high Andean Cordillera is affected by both long-range transport and by the fast-growing agglomeration of La Paz–El Alto, located approximately 20 km away and 1.5 km below the sampling site. The extended multi-year record allows us to study the properties of aerosol particles for different air mass types, during wet and dry seasons, also covering periods when the site was affected by biomass burning in the Bolivian lowlands and the Amazon Basin. The absorption, scattering, and extinction coefficients (median annual values of 0.74, 12.14, and 12.96 Mm−1 respectively) show a clear seasonal variation with low values during the wet season (0.57, 7.94, and 8.68 Mm−1 respectively) and higher values during the dry season (0.80, 11.23, and 14.51 Mm−1 respectively). The record is driven by variability at both seasonal and diurnal scales. At a diurnal scale, all records of intensive and extensive aerosol properties show a pronounced variation (daytime maximum, night-time minimum), as a result of the dynamic and convective effects. The particle light absorption, scattering, and extinction coefficients are on average 1.94, 1.49, and 1.55 times higher respectively in the turbulent thermally driven conditions than the more stable conditions, due to more efficient transport from the boundary layer. Retrieved intensive optical properties are significantly different from one season to the other, reflecting the changing aerosol emission sources of aerosol at a larger scale. Using the wavelength dependence of aerosol particle optical properties, we discriminated between contributions from natural (mainly mineral dust) and anthropogenic (mainly biomass burning and urban transport or industries) emissions according to seasons and local circulation. The main sources influencing measurements at CHC are from the urban area of La Paz–El Alto in the Altiplano and from regional biomass burning in the Amazon Basin. Results show a 28 % to 80 % increase in the extinction coefficients during the biomass burning season with respect to the dry season, which is observed in both tropospheric dynamic conditions. From this analysis, long-term observations at CHC provide the first direct evidence of the impact of biomass burning emissions of the Amazon Basin and urban emissions from the La Paz area on atmospheric optical properties at a remote site all the way to the free troposphere.

THE AEROSOLS OPTICAL PROPERTIES INVESTIGATION DURING THE DUST POLLUTION

Abstract. At present, the air environment in China is characterized by complex pollution. In this paper, the pollutant sources, transport paths and aerosol optical properties during the dust pollution was conducted to analyse based on ground-based lidar, space-borne sensor and atmospheric transmission model. Firstly, the NMMB/BSC-Dust model, the VIIRS-Suomi NPP date and HYSPLIT were carried out to analyse the dust transport paths and the dust particle size, and then the concentration of particles was analysed. Finally, the optical properties of aerosol particles in the dust weather were studied. During the formation of this weather, there is high dust in the Gobi and Taklamakan deserts. With the influence of wind direction, the dust moves from north to south, and the dust load significantly increased in southern China. Dust at the low altitude is generally transported from the Taklamakan Desert, while dust at the high altitude is generally transported from the Gobi Desert. The hourly average change of PM10 is from 36 μg/m3 to 818 μg/m3, while the hourly average change of PM2.5 is from 15 μg/m3 to 197 μg/m3. The dust was the main cause of the pollution weather. In this study, the formation process of the dust pollution revealed which can be used to provide guidance for government for the prevention work of dust pollution.

Primary sources control the variability of aerosol optical properties in the Antarctic Peninsula

Aerosol particle optical properties were measured continuously between years 2013–2015 at the Marambio station in the Antarctic Peninsula. Annual cycles of particle scattering and absorption were studied and explained using measured particle chemical composition and the analysis of air mass transport patterns. The particle scattering was found elevated during the winter but the absorption did not show any clear annual cycle. The aerosol single scattering albedo at  nm was on average 0.96 0.10, with a median of 0.99. Aerosol scattering Ångström exponent increased during summer, indicating an increasing fraction of fine mode particles. The aerosol was mainly composed of sea salt, sulphate and crustal soil minerals, and most of the particle mass were in the coarse mode. Both the particle absorption and scattering were increased during high wind speeds. This was explained by the dominance of the primary marine sea-spray and wind-blown soil dust sources. In contrast, the back-trajectory analysis suggested that long-range transport has only a minor role as a source of absorbing aerosol at the peninsula.

Aerosols dynamics in the atmosphere over Eastern Europe by means of AERONET according to weather conditions during summer 2010

Introduction. Aerosols in the Earth's atmosphere are not only air pollutants but also a factor that affects the climate. The study of the dynamics of aerosol layer properties and aerosol particles properties, and revealing sources of the atmosphere pollution by aerosols is one of the urgent problems of modern environmental sciences. Monitoring of the air pollution caused by aerosols contributes to the determination of its effects on the climate and to the reduction of its negative impacts on the health of the population.
 The purpose of this paper is to present the analysis of the dynamics of aerosols in the atmosphere over Eastern Europe. Thus, latest technologies and approaches are used: remote ground-based measurements of the optical properties of aerosol particles with the international sun photometers network AERONET; analysis of fires distribution during summer 2010 with the data application from satellite instrument MODIS; atmospheric dynamics research with the analysis of synoptic situation and modeling of transport of particles with the application of HYSPLIT model.
 Results. The peculiarities of changes of aerosol optical depth at 500 nm spectral channel and Angstrom parameter 440-870 nm for 10 AERONET stations in Eastern Europe are discussed in the article. The authors provide complex analysis of aerosols distribution together with natural processes as forest fires and overview these processes considering weather conditions that were conducive for aerosols accumulation during that time. HYSPLIT back trajectories for mentioned stations in the altitude 0.5, 1.5, 3, 4 and 5 km are used as the improvement of results of synoptic analysis. Clear advantage of modelling of transport processes give the ability to receive detailed transport paths, which makes easier to distinguish the origin of aerosols.
 Conclusion. Detailed research of aerosols with the application of up-to-date technologies makes the analysis of the optical properties of aerosols over large area quite efficient. The obvious effect of forest fires in European territory of Russia (UTR) on air quality of observational stations of Ukraine, Russia, Moldova, Romania, Poland, Belarus and Estonia is detected and analysed. The further application of satellite measurements of optical properties of aerosols are attempted to be implemented to the further research.

Studying the vertical aerosol extinction coefficient by comparing in situ airborne data and elastic backscatter lidar

Abstract. Vertical profiles of aerosol particle optical properties were explored in a case study near the San Pietro Capofiume (SPC) ground station during the PEGASOS Po Valley campaign in the summer of 2012. A Zeppelin NT airship was employed to investigate the effect of the dynamics of the planetary boundary layer at altitudes between ∼  50 and 800 m above ground. Determined properties included the aerosol particle size distribution, the hygroscopic growth factor, the effective index of refraction and the light absorption coefficient. The first three parameters were used to retrieve the light scattering coefficient. Simultaneously, direct measurements of both the scattering and absorption coefficient were carried out at the SPC ground station. Additionally, a single wavelength polarization diversity elastic lidar system provided estimates of aerosol extinction coefficients using the Klett method to accomplish the inversion of the signal, for a vertically resolved comparison between in situ and remote-sensing results. Note, however, that the comparison was for the most part done in the altitude range where the overlap function is incomplete and accordingly uncertainties are larger. First, the airborne results at low altitudes were validated with the ground measurements. Agreement within approximately ±25 and ±20 % was found for the dry scattering and absorption coefficient, respectively. The single scattering albedo, ranged between 0.83 and 0.95, indicating the importance of the absorbing particles in the Po Valley region. A clear layering of the atmosphere was observed during the beginning of the flight (until ∼  10:00 LT – local time) before the mixing layer (ML) was fully developed. Highest extinction coefficients were found at low altitudes, in the new ML, while values in the residual layer, which could be probed at the beginning of the flight at elevated altitudes, were lower. At the end of the flight (after ∼  12:00 LT) the ML was fully developed, resulting in constant extinction coefficients at all altitudes measured on the Zeppelin NT. Lidar estimates captured these dynamic features well and good agreement was found for the extinction coefficients compared to the in situ results, using fixed lidar ratios (LR) between 30 and 70 sr for the altitudes probed with the Zeppelin. These LR are consistent with values for continental aerosol particles that can be expected in this region.

Chemical apportionment of aerosol optical properties during the Asia‐Pacific Economic Cooperation summit in Beijing, China

AbstractWe have investigated the chemical and optical properties of aerosol particles during the 2014 Asia‐Pacific Economic Cooperation (APEC) summit in Beijing, China, using the highly time‐resolved measurements by a high‐resolution aerosol mass spectrometer and a cavity attenuated phase shift extinction monitor. The average (±σ) extinction coefficient (bext) and absorption coefficient (bap) were 186.5 (±184.5) M m−1 and 23.3 (±21.9) M m−1 during APEC, which were decreased by 63% and 56%, respectively, compared to those before APEC primarily due to strict emission controls. The aerosol composition and size distributions showed substantial changes during APEC; as a response, the mass scattering efficiency (MSE) of PM1 was decreased from 4.7 m2 g−1 to 3.5 m2 g−1. Comparatively, the average single‐scattering albedo (SSA) remained relatively unchanged, illustrating the synchronous reductions of bext and bap during APEC. MSE and SSA were found to increase as function of the oxidation degree of organic aerosol (OA), indicating a change of aerosol optical properties during the aging processes. The empirical relationships between chemical composition and particle extinction were established using a multiple linear regression model. Our results showed the largest contribution of ammonium nitrate to particle extinction, accounting for 35.1% and 29.3% before and during APEC, respectively. This result highlights the important role of ammonium nitrate in the formation of severe haze pollution during this study period. We also observed very different optical properties of primary and secondary aerosol. Owing to emission controls in Beijing and surrounding regions and also partly the influences of meteorological changes, the average bext of secondary aerosol during APEC was decreased by 71% from 372.3 M m−1 to 108.5 M m−1, whereas that of primary aerosol mainly from cooking, traffic, and biomass burning emissions showed a smaller reduction from 136.7 M m−1 to 71.3 M m−1. As a result, the contribution of primary aerosol to particle extinction increased from 26.8% to 39.6%, elucidating an enhanced role of local primary sources in visibility deterioration during APEC. Further analysis of chemically resolved particle extinction showed that the extinction contributions of aerosol species varied greatly between different air masses but generally with ammonium nitrate, ammonium sulfate, and secondary OA being the three major contributors.

Complex experiment on studying the microphysical, chemical, and optical properties of aerosol particles and estimating the contribution of atmospheric aerosol-to-earth radiation budget

Abstract. The primary objective of this complex aerosol experiment was the measurement of microphysical, chemical, and optical properties of aerosol particles in the surface air layer and free atmosphere. The measurement data were used to retrieve the whole set of aerosol optical parameters, necessary for radiation calculations. Three measurement cycles were performed within the experiment during 2013: in spring, when the aerosol generation is maximal; in summer (July), when atmospheric boundary layer altitude and, hence, mixing layer altitude are maximal; and in late summer/early autumn, during the period of nucleation of secondary particles. Thus, independently obtained data on the optical, meteorological, and microphysical parameters of the atmosphere allow intercalibration and inter-complement of the data and thereby provide for qualitatively new information which explains the physical nature of the processes that form the vertical structure of the aerosol field.

Optical, microphysical and compositional properties of the Eyjafjallajökull volcanic ash

Abstract. Better characterization of the optical properties of aerosol particles are an essential step to improve atmospheric models and satellite remote sensing, reduce uncertainties in predicting particulate transport, and estimate aerosol forcing and climate change. Even natural aerosols such as mineral dust or particles from volcanic eruptions require better characterization in order to define the background conditions from which anthropogenic perturbations emerge. We present a detailed laboratorial study where the spectral optical properties of the ash from the April–May (2010) Eyjafjallajökull volcanic eruption were derived over a broad spectral range, from ultra-violet (UV) to near-infrared (NIR) wavelengths. Samples of the volcanic ash taken on the ground in the vicinity of the volcano were sieved, re-suspended, and collected on filters to separate particle sizes into fine and mixed (coarse and fine) modes. We derived the spectral mass absorption efficiency αabs [m2g−1] for fine and mixed modes particles in the wavelength range from 300 to 2500 nm from measurements of optical reflectance. We retrieved the imaginary part of the complex refractive index Im(m) from αabs, using Mie–Lorenz and T-matrix theories and considering the size distribution of particles obtained by scanning electron microscopy (SEM), and the grain density of the volcanic ash measured as ρ = 2.16 ± 0.13 g cm−3. Im(m) was found to vary from 0.001 to 0.005 in the measured wavelength range. The dependence of the retrieval on the shape considered for the particles were found to be small and within the uncertainties estimated in our calculation. Fine and mixed modes were also analyzed by X-ray fluorescence, exhibiting distinct elemental composition supporting the optical differences we found between the modes. This is a comprehensive and consistent characterization of spectral absorption and imaginary refractive index, density, size, shape and elemental composition of volcanic ash, which will help constrain assumptions of ash particles in models and remote sensing, thereby narrowing uncertainties in representing these particles both for short-term regional forecasts and long-term climate change.

Study of the relative humidity dependence of aerosol light-scattering in southern Spain

This investigation focuses on the characterisation of the aerosol particle hygroscopicity. Aerosol particle optical properties were measured at Granada, Spain, during winter and spring seasons in 2013. Measured optical properties included particle light-absorption coefficient (σap) and particle light-scattering coefficient (σsp) at dry conditions and at relative humidity (RH) of 85±10%. The scattering enhancement factor, f(RH=85%), had a mean value of 1.5±0.2 and 1.6±0.3 for winter and spring campaigns, respectively. Cases of high scattering enhancement were more frequent during the spring campaign with 27% of the f(RH=85%) values above 1.8, while during the winter campaign only 8% of the data were above 1.8. A Saharan dust event (SDE), which occurred during the spring campaign, was characterised by a predominance of large particles with low hygroscopicity. For the day when the SDE was more intense, a mean daily value of f(RH=85%)=1.3±0.2 was calculated. f(RH=85%) diurnal cycle showed two minima during the morning and afternoon traffic rush hours due to the increase in non-hygroscopic particles such as black carbon and road dust. This was confirmed by small values of the single-scattering albedo and the scattering Ångstrom exponent. A significant correlation between f(RH=85%) and the fraction of particulate organic matter and sulphate was obtained. Finally, the impact of ambient RH in the aerosol radiative forcing was found to be very small due to the low ambient RH. For high RH values, the hygroscopic effect should be taken into account since the aerosol forcing efficiency changed from −13 W/m2 at dry conditions to −17 W/m2 at RH=85%.

General overview: European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) – integrating aerosol research from nano to global scales

Abstract. In this paper we describe and summarize the main achievements of the European Aerosol Cloud Climate and Air Quality Interactions project (EUCAARI). EUCAARI started on 1 January 2007 and ended on 31 December 2010 leaving a rich legacy including: (a) a comprehensive database with a year of observations of the physical, chemical and optical properties of aerosol particles over Europe, (b) comprehensive aerosol measurements in four developing countries, (c) a database of airborne measurements of aerosols and clouds over Europe during May 2008, (d) comprehensive modeling tools to study aerosol processes fron nano to global scale and their effects on climate and air quality. In addition a new Pan-European aerosol emissions inventory was developed and evaluated, a new cluster spectrometer was built and tested in the field and several new aerosol parameterizations and computations modules for chemical transport and global climate models were developed and evaluated. These achievements and related studies have substantially improved our understanding and reduced the uncertainties of aerosol radiative forcing and air quality-climate interactions. The EUCAARI results can be utilized in European and global environmental policy to assess the aerosol impacts and the corresponding abatement strategies.

Biomass burning aerosols observed in Eastern Finland during the Russian wildfires in summer 2010 – Part 1: In-situ aerosol characterization

Abstract Biomass burning smoke and associated aerosol particles from wildfires near Moscow, Russia during summer 2010 had a significant impact on air quality both in the close vicinity of the burning area and to a lesser extent in other parts of Eastern Europe. Smoke was also observed in Eastern Finland, about 1000 km northwest of the fire area, in city of Kuopio, at Puijo tower atmospheric measurement station and at the city of Kuopio air quality monitoring sites. The origin of air masses was confirmed by remote sensing observations and trajectory analyses. Despite the distance between Kuopio and the fire area and a travel time of 1–2 days, exceptional physical and optical properties of aerosol particles were evident. During smoke events, aerosol particles twice as large (geometric mean diameter 158 nm) as in background conditions (geometric mean diameter 76.3 nm) were observed and they contained record-breaking amounts of black carbon, up to 1.23 μg m −3 , which exceeds typical values by a factor of 12. Thus, absorption coefficient was significantly different when compared to background summer conditions (8.12 Mm −1 vs. 0.651 Mm −1 ). Also scattering coefficients experienced a remarkable increase, on average from 12.0 Mm −1 , 7.2 Mm −1 and 4.2 Mm −1 to 245 Mm −1 , 169 Mm −1 and 111 Mm −1 for blue, green and red light, respectively. The amount of particulate mass also experienced a multifold increase. Depending on the measurement site, PM 2.5 grew from 3 to 6 μg m −3 to 34–48 μg m −3 and PM 10 from 4 to 17 μg m −3 to 40–76 μg m −3 . Trace gas concentrations were also affected by the smoke presence, especially carbon monoxide, which is commonly used as a tracer for biomass burning smoke. The concentration of nitric oxide, nitrogen dioxide, ozone and sulfur dioxide was affected only moderately and partly masked by the emissions from local pollutant sources.

Aircraft Instrument for Comprehensive Characterization of Aerosol Optical Properties, Part I: Wavelength-Dependent Optical Extinction and Its Relative Humidity Dependence Measured Using Cavity Ringdown Spectroscopy

High-quality in situ observations of aerosol particle optical properties, namely extinction, scattering, and absorption, provide important information needed to constrain the role of aerosols in the climate system. This paper outlines the design and performance of an aircraft instrument utilizing cavity ringdown spectroscopy for the measurement of aerosol extinction. The 8-channel cavity ringdown spectrometer measures extinction at multiple wavelengths (405, 532, and 662 nm) and at multiple relative humidities (e.g., 10%, 70%, and 95%). Key performance characteristics include a 1-s detection limit better than 0.1 Mm−1, accuracy of 10 Mm−1. Laboratory and field data demonstrate that the 1-s precision is limited by the statistics of aerosol particles in the laser beam rather than the precision of the extinction measurement per se. The measurement precision improves with averaging to 5% at 60 s for extinction leve...

A novel approach for the characterisation of transport and optical properties of aerosol particles near sources – Part II: Microphysics–chemistry-transport model development and application

Abstract A new high-resolution microphysics–chemistry-transport model (LES-AOP) was developed and applied for the investigation of aerosol transformation and transport in the vicinity of a livestock facility in northern Germany (PLUS1 field campaign). The model is an extension of a Large-Eddy Simulation (LES) model. The PLUS1 field campaign included the first deployment of the new eye-safe scanning aerosol lidar system of the University of Hohenheim. In a combined approach, model and lidar results were used to characterise a faint aerosol source. The farm plume structure was investigated and the absolute value of its particle backscatter coefficient was determined. Aerosol optical properties were predicted on spatial and temporal resolutions below 100 m and 1 min, upon initialisation by measured meteorological and size-resolved particulate matter mass concentration and composition data. Faint aerosol plumes corresponding to a particle backscatter coefficient down to 10−6 sr−1 m−1 were measured and realistically simulated. Budget-related quantities such as the emission flux and change of the particulate matter mass, were estimated from model results and ground measurements.

A novel approach for the characterization of transport and optical properties of aerosol particles near sources – Part I: Measurement of particle backscatter coefficient maps with a scanning UV lidar

The physical and chemical properties of aerosols emitted from a livestock farm were determined by a novel approach which combines high-resolution lidar measurements (0.33 s, 30 m) with simulations of a microphysics–chemistry–transport model. This first of two companion papers describes the scanning lidar measurements of optical particle properties. The lidar system employed laser radiation at a wavelength of 355 nm with a power of 9 W and a pulse repetition rate of 30 Hz. The laser beam was expanded before transmission to the atmosphere so that it became eye-safe at distances >270 m to the lidar. The elastic backscatter signal was detected with a resolution of 0.033 s and 3 m. A receiving telescope with a primary-mirror diameter of 40 cm was used. For this system, we developed a novel method for two-dimensional retrievals of the particle backscatter coefficient. With this set up and approach, the lidar was able to identify the aerosol plume up to a range of ∼2.5 km from the source, a farm in northern Germany, in daytime. The measurements confirm that the optical particle properties of the emission plume vary largely with distance from the source and that the maximum particle backscatter coefficient is found away from the source. Within a close-to-horizontal scan (elevation angle of 2.3°), we found a mean particle backscatter coefficient of 1.5·10 −5 m −1 sr −1 inside the plume between 1.5 and 2.0 km distance from the source. Subtraction of the mean particle backscatter coefficient of the background aerosol present in this case (4.1·10 −6 m −1 sr −1 ) yields a particle backscatter coefficient of the livestock aerosols of 1.1·10 −5 m −1 sr −1 . The limited extend of the plume is revealed with the scanning lidar: Scans with a slightly higher elevation angle of 4.8° did not pick up the plume.