E Donev

Aerosol Lidar and in situ ozone observations of the planetary boundary layer over Bulgaria during the solar eclipse of 11 August 1999

A complex investigation of the planetary boundary layer (PBL) is presented. Observations were carried out on 11 August 1999 during the solar eclipse over Bulgaria using a Light Detection and Ranging Device (Lidar), ozone meters and ground meteorological stations. The Lidar was used to measure the height of the mixing layer before, during and after the solar eclipse in Sofia city; the ozone meters measured the surface O3 concentrations during the phenomenon, while the ground stations took meteorological parameters of the atmospheric ground layer. Weather conditions in all the regions (Sofia, Shabla, Ahtopol and Rozhen peak) were favourable for the observations. The data of the three types of measurements demonstrate with certainty that the solar eclipse affects the meteorological parameters of the atmosphere near the ground, the ozone concentration and the height of the mixing layer. It was found that a certain time delay exists in the solar eclipses impact on the meteorological parameters, the ozone concentration and the mixing layer height and that this delay was different for each of the different parameters.

Remote monitoring of aerosol layers over Sofia during Sahara dust transport episode (April, 2012)

In this work we present results of lidar remote sensing of aerosol layers in the atmosphere above Sofia during an episode of Sahara dust transport, 02-07 April, 2012. The investigations were made using two lidar systems, one equipped with a CuBr-vapor laser, emitting at wavelength 510.6 nm, and a second one - with Nd:YAG laser, at wavelengths 1064 nm and 532 nm. The results of lidar measurements are presented in terms of vertical atmospheric backscatter coefficient profiles and color maps of the aerosol stratification evolution. The involved into discussions ceilometer data (CHM 15k ceilometer) and satellite data from CALIPSO lidar, enhance the synergy of observations. Conclusion about atmospheric aerosol’s origin was made upon analyses of the information of weather-forecast maps provided by the Forecast system of Barcelona Supercomputing Centre, which are accessible via Internet. Additional information was provided by calculations of the backward air mass trajectories, using online software of NOAA about HYSPLIT model. The comparison between the data from the two lidars and the ceilometer showed similar behavior of aerosol layers development in the atmosphere above Sofia. All information about aerosol layers origin, their altitude above ground, persistence during lidar observations, confirmed the conclusion of observation of a long-distance Sahara dust transport beyond Balkans and Sofia. An interesting completion of CALIPSO lidar and ground based lidars results of measurement is presented in case of thick opaque cloud layer in the atmosphere, which slices the path of lidar sensing in both directions.

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 boundary layer observations and ozone measurements in Sofia, Bulgaria

Remote-sensing technique (aerosol LIDAR), that provides a opportunity to investigate atmospheric boundary layer structure and determine the height of the mixing layer, was used. Simultaneous observations of the convective boundary layer development and surface ozone concentration dynamics between early morning and afternoon are presented. Contribution of the two processes (photochemical ozone formation and vertical advection) driven by increasing solar radiation to ozone content is analysed on the base of experimental data received during summer campaign of 2005 in Sofia, Bulgaria. Also, simultaneous diurnal surface ozone and meteorological parameters (temperature, solar radiation, wind speed and direction, relative humidity) measurements carried out during summer - spring time of 2006 are presented. An examination of the relationships between ozone and meteorological factors provided evidence for the processes defining observed ozone pollution.

Solar eclipse: lidar, meteorological, and ozone measurements in the PBL over Bulgaria

The observations were carried out on August 11, 1999, during the solar eclipse over Bulgaria, using a lidar, an ozone meter, and ground meteorological stations. The lidar was used to measure the height of the mixing layer, in particular, before, during and after the solar eclipse in the Sofia city. The ozonemeter measured the ground ozone concentration during the phenomenon. The ground meteorological stations took the meteorological parameters of the atmopsheric ground layer. The weather conditions in all the regions (Sofia, Shabla, Ahtopol, and Peak Rozhen) were favourable for observation. The data of the three types of measurements demonstrate with certainty that the solar eclipse affects the meteorological parameters of the atmosphere near the ground, the ozone concentration, and the height of the mixing layer. It was found out that a certain time delay exists of the solar eclipse impact on the meteorological parameters, the ozone concentration and the mixing layer height, which was different for the different parameters.