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The Poland-AOD aerosol research network was established in 2011 to improve aerosol–climate interaction knowledge and provide a real-time and historical, comprehensive, and quantitative database for the aerosol optical properties distribution over Poland. The network consists of research institutions and private owners operating 10 measurement stations and an organization responsible for aerosol model transport simulations. Poland-AOD collaboration provides observations of spectral aerosol optical depth (AOD), Ångstrom Exponent (AE), incoming shortwave (SW) and longwave (LW) radiation fluxes, vertical profiles of aerosol optical properties and surface aerosol scattering and absorption coefficient, as well as microphysical particle properties. Based on the radiative transfer model (RTM), the aerosol radiative forcing (ARF) and the heating rate are simulated. In addition, results from GEM-AQ and WRF-Chem models (e.g., aerosol mass mixing ratio and optical properties for several particle chemical components), and HYSPLIT back-trajectories are used to interpret the results of observation and to describe the 3D aerosol optical properties distribution. Results of Poland-AOD research indicate progressive improvement of air quality and at mospheric turbidity during the last decade. The AOD was reduced by about 0.02/10 yr (at 550 nm), which corresponds to positive trends in ARF. The estimated clear-sky ARF trend is 0.34 W/m2/10 yr and 0.68 W/m2/10 yr, respectively, at TOA and at Earth’s surface. Therefore, reduction in aerosol load observed in Poland can significantly contribute to climate warming.

Characterization of small-scale temperature structure of convective clouds and their environment is crucial to understand turbulent entrainment, mixing and its effect on cloud dynamics and microphysics. A newly constructed ultra-fast thermometer UFT2, developed from the former UFT-M, allowing for temperature measurements in clouds with the resolution better than few centimeters, was deployed on the British Antarctic Survey Twin-Otter research aircraft in the course of the EUREC4A research campaign. The goal was to perform first ever fine-scale temperature characterization of subtropical marine warm cumulus clouds.The prototype instrument worked relatively well and allow to collect data from 7 of 17 research flights, including hundreds of cloud penetrations and segments of flights in the marine surface layer. Data, collected with 20 kHz sampling rate, after filtering and averaging allowed to achieve physical resolution of ~3cm at ~60m/s true air speed of the aircraft.Performance of the UFT-2 sensor and its calibration will be discussed. The discussion will be illustrated with examples of multi-scale temperature records collected in cloud interiors, cloud edges, cloud shells at various altitudes as well as in the marine surface layer ~30 m above the sea level.

The science guiding the EUREC4A campaign and its measurements is presented. EUREC4A comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic – eastward and southeastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EUREC4A marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200 km) and larger (500 km) scales, roughly 400 h of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced ground-based cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10 000 profiles), lower atmosphere (continuous profiling), and along the air–sea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EUREC4A explored – from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation – are presented along with an overview of EUREC4A's outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplement.

This work presents the methodology for obtaining the vertical profiles of aerosol optical and microphysical properties based on cable-car and ground-based measurements in a mountain region. The presented data were collected during the winter workshop between 7th and 13th March 2016 in Krynica-Zdroj (southern Poland). During this campaign photoacoustic instruments were used to observe the single-scattering optical properties at two sites with a vertical separation distance of about 360 m. The micro-aethalometer AE-51 and the optical particle counter OPC-N2 were mounted on the cable car and used to measure profiles of black carbon concentration and aerosol size distribution. The mean extinction coefficients at the upper (37 Mm −1 ) and lower (43 Mm −1 ) sites were about three times lower than the long-term average for this season due to weather conditions, which did not favour the haze conditions. However, a significant correlation between temperature gradient and difference of extinction coefficient between the valley and mountain was found. During nights and stable thermodynamic conditions the values in the valley were higher than close to the top of the mountain. Profiles obtained from cable car measurements shown significant reduction of black carbon and aerosol concentration with altitude also during the day time. In addition, the effective radius, and the fine and coarse mode aerosol concentration was slightly changed with altitude when the relative humidity was below 100%. During condensation and cloud formation the significant variability in particles effective radius were found as a result of aerosol activation close to the top of the mountains.

This study presents the vertical profiles of aerosol optical and microphysical properties obtained from cable car and ground-based measurements in the Silesian Beskids, Poland. The data were collected during a measurement campaign between 25 February and March 11, 2018. An AE-51 micro-aethalometer and PMS7003 and OPC-N2 optical particle counters were mounted on the cable car and used to measure the profiles of equivalent of black carbon (eBC) concentration and aerosol size distribution. In situ measurements of the optical properties of the aerosols were obtained using an AE-31 aethalometer and photoacoustic devices. A prototype lidar was used to determine the planetary boundary layer (PBL) height and the aerosol layers. In the middle phase of the study (1–6 March 2018), significant night-time temperature inversions were observed. During the inversion period, the parameters describing the amount of aerosols in the air increased significantly. The concentration of eBC exceeded the level of 15 μg/m3 several times, with an average level of 5.39 ± 4.42 μg/m3. Conversely, the results obtained in the first and third phases of the experiment were at the level of the aerosol background, being 1.45 ± 0.88 μg/m3 and 0.90 ± 0.95 μg/m3, respectively. Significant differences were also observed in the vertical profiles of PM10 mass and eBC concentration. In the middle phase of the study, the profiles showed a significant reduction in the concentration of pollutants with height, while in the first and third phases, there were slight variations with height.

Specific aerosols and cloud properties over large urban regions seem to generate an island, similar to the well-known urban heat island, leading to lower ultraviolet (UV) radiation intensity compared to the surrounding less polluted areas, thus creating a shield against excessive human exposure to UV radiation. The present study focuses on differences between erythemal and UVA (324 nm) doses measured by the Brewer spectrophotometers in Warsaw (52.3° N, 21.0° E) and Belsk (51.8° N, 20.8° E). The latter is a rural region located about 60 km south-west of the city. Ratios between erythemal and UVA partly daily doses, obtained during all-sky and cloudless-sky conditions for the period May 2013–December 2015, were analysed to infer a specific cloud and aerosol forcing on the surface UV doses over Warsaw. Radiative model simulations were carried out to find sources of the observed differences between the sites. It was found that Warsaw urban agglomeration induced 8 and 6 % attenuation of the erythemal and UVA doses respectively. This is mostly due to the lower sun elevation in Warsaw during the near-noon measurements and the larger optical depth of the city aerosols and increased cloudiness. It could be hypothesised that the expected stronger absorption of the solar UV radiation by urban aerosols is compensated for here by a higher surface reflectivity over the city.

The subject of this study is to use in-situ measurements, passive and active remote sensing observations, as well as numerical simulations to describe the temporal variability of aerosol single-scattering properties such as aerosol optical depth (AOD), single scattering albedo (SSA), and aerosol direct shortwave forcing at the Earth׳s surface during the transport of biomass burning (BB) aerosols from Canada to Europe between 2nd and 7th of July 2013. According to the MODIS observations made in the IR spectrum, an area of over 200,000 km 2 was affected by the BB during the episode. Regarding the AERONET data in Canada, results show a significant variability of AOD within the whole period with a special enhancement between 6th and 9th July, when AOD anomaly led to an increase up to 1.5 (500 nm). Low-values of SSA reported at Yellowknife Aurora and Waskesiu are likely to be due to flaming combustion from closely located source areas. MODIS and CALIPSO observations, as well as numerical simulations of the NAAPS model, show transport of smoke particles over the Northern Atlantic Ocean and further eastward. Indeed, the event was observed at a different times and locations over Europe between 2nd and 14th July. During that period a number of AERONET stations, mainly located close to the Baltic Sea reported AOD at 500 nm of above 1. Compared to Canada the SSA in Europe was higher, indicating particle transformation over the Atlantic Ocean. Lidar observations in the northern Poland showed aerosol layers occurring between PBL height and tropopause with a significant (up to 55%) contribution to the total AOD. However, lidar measurements in Central Poland (Warsaw and Belsk) indicate that aerosols were confined mainly in the middle and lower troposphere. A diurnal mean aerosol direct radiative forcing estimated at the ground level during the event was below −30 W/m 2 with radiative forcing efficiency between −60 and −100 W/m 2 /τ 500. The strongest efficiency was found at the Strzyzow station, which was caused by further air mass transformation during its transport over Poland.

Measurements of the Linke turbidity factor (LTF) were performed at Belsk (20.78°E, 51.83°N), Poland, since 1964. This data is used to retrieve broadband aerosol optical thickness normalized to the air mass equal to 2 (BAOT2). A linear analysis of the BAOT2 changes reveals an upward trend of 0.023±0.017(2σ) in the 1964–1975 period, a downward trend of–0.051±0.017(2σ) in the 1976–1991 period, and afterwards a statistically insignificant trend of–0.009 ± 0.014(2σ). Such pattern may be related to the economic changes in Poland (changing emissions and environmental policies). The elevated BAOT2 values, excluded from the trend, are found in 1984 and 1992 due to the volcanic eruptions of El Chichon and Mt. Pinatubo, respectively. Past AOT values at 340 and 500 nm are reconstructed using a linear relationship found between AOT and BAOT2. The reconstructed data is used by the radiative transfer models to estimate a response of the total solar and erythemal radiation to the changes in the atmospheric aerosols at Belsk.

Software to retrieve profiles of aerosol particle size distribution (APSD) from multiwavelength lidar signals is presented. The approach consists in direct fit of artificial signal generated using predefined distribution to the experimental signals. Combination of two lognormal functions with a few free parameters is applied for the predefined APSD. The minimization technique allows finding lognormal function parameters which provide the best fit. The approach was tested on the experimental signals registered at 1064, 532 and 355 nm. The software is designated for processing on PCs. The computation time was about several minutes. Program summary Program title: APSD_Software Catalogue identifier: AEXV_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEXV_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: Open Licence No. of lines in distributed program, including test data, etc.: 12813 No. of bytes in distributed program, including test data, etc.: 878099 Distribution format: tar.gz Programming language: Delphi 2010. Computer: PC. Operating system: Windows XP, Vista, 7, 8, 8.1. RAM: 37MB Classification: 13. Nature of problem: Aerosol Particle Size Distribution (APSD) is a very significant function for evaluation of atmospheric optical properties. Remote determination of APSD might be performed with multiwavelength lidar. Retrieval of profiles of APSD from multiwavelength lidar signals is an example of ill-posed problem in the atmospheric physics (in the sense of Jacques Hadamard). Solution method: The approach consists in direct fit of artificial signals to the experimental signals. The artificial signals are generated using predefined aerosol particle distribution, Combination of two lognormal functions with a few free parameters is applied for the predefined APSD. The minimization technique used in the software allows finding lognormal function parameters which provide the best fit. Additional comments: The input signal should be located into the SIGNALS directory which is automatically created by the software. The results are presented in the main form of the software. They are also saved into the same directory from which it was loaded input file. They are saved as a BitMap as well as the ASCII files. The software returns two main sets of files: first one “APSD.bmp” and “APSD_Iet.txt”, and the second one “EffectiveRadius.bmp” and “EffectiveRadius.txt”. Running time: 195 s for an input file consisting 12 measurement points (altitudes).

The properties of atmospheric aerosol under a cumulus base were studied using three-wavelength lidar. A growth of hygroscopic aerosol particles in a convective updraft and the activation of cloud condensation nuclei (CCN) were observed. A simple and robust model of droplet formation in a rising parcel was used as a closing assumption to the original approach of cloud droplet number concentration (CDNC) retrieval. The potential to retrieve the vertical profile of the effective radius of droplets near the cloud base and the height of activation and condensation of nuclei is demonstrated.

Two significant volcanic eruptions, i.e., Eyjafjallajokull (April–May 2010) and Grimsvotn (May 2011) took place recently in Iceland. Within a few days after eruptions, layers of high aerosol concentration have been observed by multiwavelength lidar of the Polish Polar Station at Hornsund, Svalbard. Measurements of the aerosol’s optical properties indicated a possible presence of volcanic ash transported over the Station. The latter presumption was confirmed by the computed backward trajectories of air masses, showing their paths passing over the location of volcanoes.

This work provides information on selected optical parameters related to volcanic ash produced during the eruption of the Eyjafjoll volcano in Iceland in 2010. The observations were made between 16 and 18 April 2010 at four stations representative for northern (Sopot), central (Warsaw, Belsk) and south-eastern (Strzyzow) regions of Poland. The largest ash plume (in terms of aerosol optical thickness) over Poland was observed at night of 16/17 April 2010 in the layer between 4 and 5.5 km a.s.l. The highest values of the aerosol extinction coefficient reached 0.06e0.08 km � 1 at 532 nm (based on lidar observations in Warsaw) and 0.02e0.04 km � 1 at 1064 nm (based on ceilometer observations in Warsaw). The corresponding optical thickness due to volcanic ash reached values of about 0.05 at 532 nm and about 0.03 at 1064 nm. These values are similar to those reported for the Belsk station based on lidar observations. The ash mass concentration estimated based on the maximum aerosol extinction coefficient reached 0.22 � 0.11 mg m � 3 . This value is significantly lower than the limit (2 mg m � 3 ) for the aircraft operation.

This paper presents the measurements of a vertical structure of aerosol optical properties performed during the MACRON (Maritime Aerosol, Clouds and Radiation Observation in Norway) campaign, which took place in July and August 2007 at ALOMAR observatory on Andoya island (69.279°N, 16.009°E, elevation 380 m a.s.l.). The mean value of the aerosol optical thickness (AOT) at 500 nm during campaign was 0.12. Significant increase of the AOT above longtime mean value was observed on 7 and 8 August 2007 when the AOT exceeded 0.4 at 500 nm. Analyses of back trajectories show the aerosol transported from over Africa and Central Europe. The aerosol extinction coefficient obtained from the synergy of ceilometer and sun photometer observations reached 0.05-0.08 km –1 (at 1064 nm) in the dust layer. The single scattering

A simple and safe lidar system based on a nitrogen laser (337.1 nm) is described. The setup permits undergraduates to learn the principles and applications of the lidar technique. The apparatus is used for exercises about measurements of distance to objects, the determination of light velocity as well as about retrieving the back-scatter coefficient of a water aerosol cloud. The system may also be used for demonstrating the principle of fluorescence lidar.

In this paper, optical measurements of aerosol properties made during a ship cruise from Poland to Antarctic Station in September and October 2006, and during the cruise back to Gdynia in April and May 2007 are described. A large gradient of pollution between the clear South Atlantic and the dusty North Atlantic was observed. The maximum of aerosol optical thickness at a wavelength of 500 nm reached 0.4 at 20°N in September 2006 and 0.3 at 40°N in May 2007, respectively. Strong Saharan dust transport is suggested as an explanation for the small values of Angstrom exponent observed (values of 0.2 and 0.4 on these respective dates). On the Southern Hemisphere the aerosol optical thickness at 500 nm ranged from 0.05 to 0.2. Significant increases of the aerosol optical thickness were associated with strong wind and sea salt production. Good agreement was found when the in situ measurements of aerosol optical thickness were compared to satellite retrievals and modelling results.

A cluster analysis is applied to the Aerosol Robotic Network (AERONET) data obtained at Belsk, Poland, as well as three nearby Central European stations (Leipzig, Minsk and Moldova) for estimation of atmospheric aerosol types. Absorption Ångstrom exponent (AAE), aerosol optical thickness (AOT) and extinction Ångstrom exponent (EAE) parameters are used. Clustering in both 2D (AOT, EAE) and 3D (AOT, EAE, AAE) is investigated. A method of air mass backward trajectory analysis is then proposed, with the receptor site at Belsk, to determine possible source regions for each cluster. Four dominant aerosol source regions are identified. The biomass burning aerosol source is localized in the vicinity of Belarusian-Ukrainian border. Slovakia and northern Hungary are found to be the source of urban/industrial pollutants. Western Poland and eastern Germany are the main sources of polluted continental aerosols. The most differentiated source region of Scandinavia, Baltic Sea and Northern Atlantic, associated with lowest values of AOT, corresponds to clean continental and possibly maritime type aerosols.

In the paper application of lidars for investigation of aerosol particle size distribution and for observation of aerosol consisting of solid state particles is presented. For size distribution the multiwavelength lidar and original method of data analysis was applied. For registration of dust transported to Central Europe from Sahara and Middle East deserts analysis of depolarization of the backscattered signals was used. In order to solve the lidar equation measurements of total atmospheric optical depth by means of Microtops sun photometer was done. Mean size and the aspect ratio of dust particles were determined by comparing of lidar observations with data from T-matrix calculations.

Multiwavelength micropulse lidar (MML) designed for continuous optical sounding of the atmosphere is presented. A specific signal processing technique applying two directional Kalman filtering is introduced in order to enhance signal to noise ratio. Application of this technique is illustrated with profiles collected in course of COAST 2009 and WRNP 2010 research campaigns.

Results of measurements of atmospheric aerosol performed with multiwavelength lidar are presented. An approach to retrieve profiles of aerosol particle size distribution was elaborated. It consists in direct fit of predefined distribution (usually combination of lognormal functions with a few free parameters) to the experimental signals. The approach was used for retrieving marine aerosol distributions. Studies of behavior of the particles at the cumulus cloud base were performed as well. There the assumptions based on Twomey's model of the adiabatic parcel were used to support the retrieving technique which was adopted to analyze lidar profiles (at 355, 532 and 1064 nm wavelengths) registered in the region of the base of small warm cumulus clouds. Size distribution profiles and changes of particle effective radius within the range of 0.5 - 3 μm were discussed.

A method of retrieval of the aerosol particle size distribution (APSD) from multiwavelength lidar signals is presented. Assumed distribution (usually a bimodal combination of lognormal functions) with a few free parameters is directly substituted into the lidar equations. The minimization technique allows one to find the parameters that provide the best fit of the assumed APSD by comparison of theoretically generated and experimental signals. Prior knowledge of the lidar ratio is not required. The approach was tested on a typical synthetic APSD consisting of spherical droplets. Comparison of lidar measurements with results from a condensation particle counter was also performed. For signals registered at 3-5 wavelengths from the UV to the near IR a satisfactory retrieval of synthetic APSD is possible for the particles within the 100-3000 nm range.