Tsvetina Evgenieva

Optical characteristics of aerosol determined by Cimel, Prede, and Microtops II sun photometers over Belsk, Poland

An experimental campaign was carried out at Central Geophysical Laboratory at Belsk (Poland) in October 2007. Three sun photometers: Cimel CE-318, Prede POM-01L and Microtops II were used to obtain the atmospheric aerosol optical characteristics. Cimel CE-318 and Prede POM-01L are automatic sun-tracking devices common in the world networks for aerosol investigations AERONET and SKYNET. Microtops II is a hand-held manual device often used in field experiments because of its mobility. The results obtained show similar behavior of the aerosol optical depth variations and close values obtained by the three devices at the common wavelengths over rural area. The Microtops II readings are between the readings of the other two sun photometers. The experiment carried out is helpful and shows that the Microtops II sun photometer provides comparable results to these obtained by the Cimel CE-318 and Prede POM-01L sun photometers and potential of using Microtops II for measurement over an urban and rural area.

Boundary layer development and meteorological parameters impact on the ground level ozone concentration over an urban area in a mountain valley Sofia, Bulgaria

The ecological problems caused by the increasing ozone concentration are not easily solved because ozone is not directly emitted by certain sources Its concentration depends on numerous dynamical and chemical processes. Stratosphere–troposphere exchange and subsequent ozone penetration into the boundary layer determine the contribution of so-called ‘natural’ ozone to ozone pollution near the ground. However, the main contribution to the concentration of this pollution is that of the anthropogenic ozone, which is generated as a result of complex photochemical reactions. The purpose of this research is the ground level ozone concentration behaviour to be studied during the stable boundary layer (SBL) and the residual layer (RL) destruction and the convective boundary layer (CBL) formation, so the influence of the temperature, the relative humidity and the height of the mixing layer (ML) as well as that of the ML formation in different areas of Sofia (42° 39′ N, 23° 23′ E, 591 m above sea level), Bulgaria, have to be determined. The ground level ozone concentration in the area of the Institute of Electronics changes synchronously with the development of the ML. The maximum values of the ground level ozone concentration are reached when the height of the ML reached its maximum and afterwards. The maximum growth of the ground level ozone concentration is around 11:00–12:30 h LST when a fast growth of the ML begins and the complete destruction of the RL is observed, that is, the two processes of ML growth and entrainment of aerosol and ozone from the higher layers of the atmospheric boundary layer are observed. The values of the ground level ozone concentration during the summer months are higher than those during the fall.

Surface and total ozone investigations in the region of Sofia, Bulgaria

Atmospheric ozone behaviour over Sofia has been investigated with remote-sensing and in situ techniques. Surface ozone and boundary layer observations performed in recent years at three city sites have been analysed. It was found that, in the autumn period, at close meteorological conditions, diurnal ozone variations show stable behaviour from year to year during the analysed period. It may be assumed that the boundary layer and ozone precursor concentrations, which are involved in photochemical ozone formation, keep up their state from year to year at the mentioned conditions. These findings may be interesting when surface ozone trends and climate change influence on ozone are investigated. The analysis of the long-term total ozone content (TOC) variations did not find a total ozone trend in the 1997–2008 period.

Case study of the ABL height and optical parameters of the atmospheric aerosols over Sofia

A study of the atmospheric boundary layer (ABL) height and its relation to the variations in the aerosol optical depth (AOD), Ångström coefficients, water vapor column (WVC) and total ozone column (TOC) was carried out in June 2011 and June 2012 at three sites in the city of Sofia (Institute of Electronics, Astronomical Observatory in the Borisova Gradina Park and National Institute of Geophysics, Geodesy and Geography). A ceilometer CHM15k, a sun photometer Microtops II, an ozonometer Microtops II and an automatic meteorological station were used during the experiments. Measurements of the AOD, WVC and TOC were done during the development of the ABL (followed by the ceilometer). In order to access microphysical properties of the aerosols, the Ångström coefficients α and β were retrieved from the spectral AOD data by the Volz method from three wavelength pairs 500/1020nm, 500/675nm and 380/1020nm. Comparison was done between the results obtained. Daily behavior of the AOD, Ångström exponent α and turbidity coefficient β, WVC and TOC are presented. Different types of AOD and WVC behavior were observed. The AOD had maximum values 1-2 h before ABL to reach its maximum height for the day. No significant correlation is found between TOC daily behavior and that of the AOD and WVC.

Ceilometer, sun photometer and ozonometer measurements of the aerosol optical depth,angstrom coefficients, water vapor and total ozone content over Sofia (Bulgaria)

This article presents the results of a study related to variations in aerosol optical depth, total ozone content, water vapor content and angstrom coefficients from three experimental campaigns carried out in June 2010, June 2011and June 2012 at three sites in the city of Sofia (Institute of Electronics, Astronomical Observatory in the Borisova Gradina Park and National Institute of Geophysics, Geodesy and Geography (NIGGG)). A ceilometer CHM15k, two sun photometers Microtops II and an automatic meteorological station were used during the experiments. The height of the mixing layer varied from 1500m to 2500 (3000)m during the measurements. The height of the residual layer ranged from 800m to 2000m. The stable boundary layer extended to 200-400m over the campaigns. The aerosol optical depth (AOD) at wavelength λ = 500nm ranged from 0.38 to 0.66 in the first campaign and from 0.24 to 0.55 in the second one and from 0.11 to 0.23 in the third one. Corresponding ranges for the water vapor content (WVC) were 1.26cm to 2.6cm. Different types of aerosol optical depth and water vapor content behavior were observed. Additional resource of information about the origin of the aerosol layers detected by the ceilometer CHM15k offered the HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) model. The calculations of backward air mass trajectories give a plot of the road that the air mass traversed for a chosen time period before to arrive to the location of Sofia city. The total ozone content (TOC) varied from 240 DU to 370 DU during the campaigns. The ground - based observation from ozonemeter Microtops II with satellite observation of Ozone Monitor Instruments (OMI) over Sofia (Bulgaria) are compared. Our results have implications for the further study of regional climate variability.

Lidar observations of long-range transported Saharan dust over Sofia, Bulgaria: a case study of dust mixed with local aerosols

Abstract. Two-wavelength (1064/532  nm) lidar observations of long-range transported Saharan dust present in the atmosphere over Sofia, Bulgaria, during a 4-day dust intrusion event in winter 2010, are reported. Aged desert aerosols are detected at altitudes up to 4 km above the sea level, within and above the boundary layer as mixed with other aerosols—representing the particular case under consideration. Optical, microphysical, and dynamical properties of dust aerosols are obtained and analyzed. Special attention is paid to retrieving and vertical profiling of dust backscatter-related Ångström exponents (BAEs), as well as to determining their frequency-count distributions. Obtained BAE values in the range 0.3 to 0.6 (±0.2) indicate domination of coarse particles in the near overmicron size range. Reasonability of coarse-mode-dominated dust size composition is substantiated, based on measurement and transportation-history analysis. The performed frequency-count statistics reveals dust BAE distributions asymmetrically extended to multimode distribution shapes, resulting from dust mixing with finer local aerosol fractions. Peculiarities and patterns of the aerosol dynamics at different stages of dust-loading event are revealed and discussed.

Ångström coefficients calculated from aerosol optical depth data obtained over Sofia, Bulgaria

One year (October 2006 – October 2007) continuous measurements of the aerosol optical depth (AOD) during the development of planetary boundary layer (followed by lidar) were carried out by a sun photometer Microtops II over the city of Sofia, Bulgaria. In order to asses aerosols microphysical properties, the Angstrom coefficients α and β are retrieved from the spectral AOD data using the Volz method. Daily behavior of AOD, Angstrom exponent α and turbidity parameter β as well as their monthly mean variations are presented. Variations in the monthly mean AOD at λ = 500 nm, α and β (computed from the wavelength pair 500/1020 nm) had similar behavior. The mean values of the AOD, α and β for the whole period (October 2006 –October 2007) are found to be 0.28±0.07, 1.21±0.17 and 0.11±0.03, respectively, as highest values of the AOD (0.42±0.21), α (1.62±0.53) and β (0.17±0.10) were obtained in August 2007. The lowest monthly mean AOD, α and β were 0.21±0.09 (in January and February 2007), 1.03±0.42 (in April 2007) and 0.09±0.04 (in January and October 2007), respectively. In addition, Angstrom coefficients α and β are calculated from the wavelength pair 500/675 nm and comparison is done between the results obtained from the two wavelength pairs. The above mentioned values reveal low to moderate turbidity of the atmosphere and dominance of fine-mode aerosols over the city of Sofia associated with heavy vehicular traffic and local anthropogenic pollution sources.

Two-wavelength lidar characterization of optical, dynamical, and microphysical properties of Saharan dust layers over Sofia, Bulgaria

In this work, we present results of two-wavelength lidar observations on Saharan dust layers over Sofia, Bulgaria, in two days of strong dust intrusion events in the fall and winter of the year 2010. Measurements are carried out at two wavelengths (1064 nm and 532 nm) by using two channels of an aerosol lidar based on a frequency-doubled Nd:YAG laser. Optical, dynamical, and microphysical properties of the dust layers are studied and analyzed, distinguishing specifics of coarse and fine aerosol fractions. The spatial-temporal evolution of atmospheric aerosol/dust density fluctuations is shown on height-time coordinate color-map plots for each of the two wavelengths. Time-averaged height profiles of the atmospheric backscattering coefficient at 1064 nm and 532 nm are presented, showing the dust and aerosol density distribution up to about 10 km AGL, with a range/height resolution of 15/8 m. Microphysical properties of dust and aerosol particles are characterized qualitatively by using backscatter-related Ǻngström exponents (BAE). Range-resolved time-averaged height profiles of BAE are shown, particularly for the dust layers, indicating the dominating particle size-modes. Obtained BAE values in the range 0.2-0.5 are typical for desert mineral dust, suggesting coarse particles in the over-micron size range. Frequency-count analysis of the obtained BAE arrays is performed for typical separate dust-containing layers, revealing distributions and changes of particle size modes in terms of BAE, as well as effects of dust mixing with finer urban and industrial aerosols. Some efforts are devoted and focused on characterizing the temporal dynamics of the range distribution and density of dust and aerosols. Peculiarities of spatial distribution, size composition, and temporal evolution of Saharan dust aerosols are revealed, analyzed, and discussed.

Ceilometer observation of Saharan dust over mountain valley of Sofia, Bulgaria

Atmospheric aerosol is known to considerably influence the Earth’s radiative budget and to make an impact on air quality. The influence of aerosols strongly depends on their spatial distribution and optical properties. The aerosol has natural and anthropogenic origin. Aerosol types can be also classified according to their size, sources or geographical origin (desert, continental, marine etc.). Mineral dust is one of the natural aerosols presented in the atmosphere. Its main source is the Sahara desert region. Saharan aerosol layers are frequently observed in Europe by means of active and passive remote sensing devices, especially in the frame of EARLINET and ACTRIS 3, 5, 6, 7, 8, 9. In this paper, observations of vertical distribution of aerosols and assessment of their optical properties will be presented. Two-year (2013-2014) complex measurements were carried out by a ceilometer CHM-15k (Jenoptic) and two lidars in an urban area located in a mountain valley (Sofia, Bulgaria)1. The ceilometer works 24 hours in automatic mode. Part of the results is compared with results obtained by lidars operating in photon counting modes for specific periods of simultaneous work5. Supplementary data from: two meteorological stations; HYSPLIT back trajectory model4; BSCDREAM8b dust model9; and the database of atmospheric radio sounding profiles from Department of Atmospheric Engineering of Wyoming University (USA) are also used in the analysis of the obtained results.

Summer lidar measurements in the troposphere over ALOMAR, Norway in 2007

Aerosol structure measurements in the troposphere were carried out at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR), Norway, during summer 2007. ALOMAR troposheric lidar and Cimel CE-318 sun photometer were used to implement the aerosol measurements. Three wavelengths of the sounding laser radiation were used during the experiment λ1=1064nm, λ2=532nm and λ3=355nm which brings additional information about atmospheric aerosol optical and microphysical characteristics in the whole troposphere. The experimental data could be arranged in two groups: days when Ci-clouds were observed (in June) and days when the meteorological situation is characterized with clear sunny weather (in the beginning of July). In days with presence of Ci-clouds two layers are observed in the planetary boundary layer-the first one with maximum height from 1500m to 2000m; the second one with maximum height from 2000m to 3000m. In clear sunny days few layers are observed with minimum height from 1500m to 2300m and maximum height around H=6000m. The height of the layers remains constant or decrease with time. The lidar data are juxtaposed with the data obtained by the sun photometer.