Vera Grigorieva

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.

Influence of the boundary layer development on the ozone concentration over an urban area

Results obtained during two campaigns (summer 2004 and autumn 2005) of observation of the planetary boundary layer dynamics over the Sofia city urban area are presented. An EARLINET scanning aerosol lidar, an ozone analyser and a ground meteorological station were used during the observations. The stable boundary layer height varied from 200 m to 600 m during the different seasons. The residual layer was found to be at 700–1200 m, being destroyed between 10:30 and 12:30 LST. The mixing layer developed up to heights of about 800–1300 m. The ground level ozone concentration was measured to be from 10 µg/m3 to 90 µg/m3. The convective boundary layer formation in three case studies (a clear sunny day, a partial solar eclipse, and in the presence of internal atmospheric gravity waves) are presented. In particular, the mixing layer development and the residual layer destruction are studied and considered, along with the relevant ground level ozone concentration variation.

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.

The possible uncertainties over quality of the surface ozone data

Ozone is one of the main air pollutants. Now it is suggested that a positive trend of tropospheric ozone concentrations takes place. The question concerning the quality of ozone data, from which O3 trend is evaluated, is very important because on base of this trend are accepted the political and economical decisions directed at ozone pollution reduction. Two methods (ultra-violet optical absorption and chemiluminescence) for surface ozone measurements have been analyzed with respect to the quality of O3 data. The review shows that the ultra-violet (UV) optical absorption method may be influenced by positive interferences from other atmospheric components. It appears that the chemiluminescence method is more interference free.

Peculiarities in the diurnal variations of surface ozone in the Pamir mountains

The first summertime observations of surface ozone have been made in the Pamir mountains, Central Asia. Measurements of the O3 concentrations were performed at six valley sites situated in the Northern Pamirs at altitudes of 1500–4000 m above sea level. The peculiarities of the diurnal ozone variations and the processes responsible for them are analysed. The observed diurnal variations are common to all sites, considerable and show a minimum in the night (5–10 ppb) and a maximum in the daytime (up to 35 ppb). The character of the diurnal cycles is typical for valley sites and is associated closely with mesoscale mechanisms – mountain‐valley circulation and local temperature regime. The low night‐time O3 concentrations are caused by dry ozone deposition to the ground under nocturnal temperature inversions and by strong O3 destruction in the air streaming to the valley with downslope wind. Due to the low level of anthropogenic factors in the Pamir valleys, there was no experimental evidence of the significant contribution of the local photochemical O3 production to detected ozone concentrations. It is believed that measured daytime ozone concentrations are representative of lower tropospheric background ozone ones. The rarely studied short‐term ozone variations observed during the measuring campaign are also presented.

Investigation of correlations between the high surface ozone episodes and the stratospheric intrusion events

This paper presents a study of the role of direct O3-rich stratospheric intrusions in the high ozone episodes observed near the ground. The close analysis of the experimental data and the criteria characterizing the intrusion events shows that stratsopheric air injections can contribute to the spring-time ozone maximum and that during summer time the peak surface ozone concentration can have not only a photochemical origin (which is usally associated with local or regional anthropogenic ozone precursor pollution) but also and a stratospheric origin.

Lidar, Radiometer and Ozonemeter Measurements over Urban Area

A scanning aerosol lidar, a NIR‐VIS radiometer, an ozonemeter and a ground meteorological station were used for observation of the atmosphere over the urban area of the Sofia City. The mixing layer height and the aerosol extinction coefficient and its variation during the convective boundary layer formation are determined using the lidar data. The spectral dependence of the extinction coefficient is estimated by means of the radiometric data.

Variations in the ozone concentration during the boundary layer development over urban area

Some results obtained during two campaigns (summer 2004 and autumn 2005) of observation of the planetary boundary layer dynamics over the urban area of the Sofia city are presented. An EARLINET scanning aerosol lidar, an ozone analyzer and a ground meteorological station were used during the observations. Particularly, the mixing layer development and the residual layer destruction along with the relevant ground level ozone concentration variation followed during the convective boundary layer formation in two situations (in the case of a partial solar eclipse, and in the case of atmospheric internal gravity waves presence) are presented and considered.

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.