BEO Moussala – INRNE – BAS


The Basic Environmental Observatory (BEO) Moussala is situated at the highest peak on the Balkan Peninsula – Moussala (2925.4 m a.s.l., 42° 10’ 45’’ N, 23° 35’ 07’’ E) in the Rila Mountain – the central part of the Bulgarian southern mountain area. It is a facility with modern infrastructure for scientific investigations.

The Observatory is in the free troposphere most of the time which permits providing of the unique experiments and monitoring of local and trance boundary pollutants. Data are stored for real-time retrieval, performing the retrospective analyses and modeling.


BEO Moussala is a two-story building with a total built-up area of 348 m2. On the ground floor, there are two laboratories and two bedrooms. On the same floor there is a kitchen with a host room, two bathrooms and two storage rooms. Upstairs there are two laboratories, a conference room and a small bedroom. It goes to a measuring ground on which are located the apparatuses which are designed for open-air operation.

The whole building is packed with metal panels that form a Faraday cage. Outside of the main building, there are premises for the automatic diesel generator and the fuel reserve. BEO Moussala is protected with active lightning protection. It has own internet connection through an antenna directed towards the building of INRNE-BAS, Sofia.

General Device Description

The BEO Moussala is a research complex and data quality is an issue which remains in the focus needing persistent and continuous efforts.

The devices for cosmic rays research, the Automatic Weather Station (AWS), the gas and aerosol measurement systems allow to carry out precise study of the atmosphere parameters and cosmic rays. The connection between the atmospheric events and the cosmic ray flux is prospective field for investigation.

The BEO Moussala information system including the measurement systems, the high frequency telecommunication system and the database can be used in situ or by remote access of the international scientific community.

The BEO Moussala has a long tradition as a high mountain scientific facility and its future, mostly depends on the process of scientific collaboration and integration in the global research area.

The study of high mountain environmental parameters (meteorology, atmospheric physics and chemistry, background radiation, and cosmic rays) measured at BEO Moussala gives the possibility for complex evaluation of anthropogenic and biogenic impacts on the climate.

Aerosols Devices


Сканиращ аерозолен спектрометър – САС

The measurement of particle number size distributions is one of the most important tasks describing the physical properties of aerosol particles. Particles show large variation in number and size depending on their location of occurrence. In the last decade, a number of groups has started to measure particle number size distributions at various locations over the world by operating measurement devices continuously. A typical measurement device for providing particle number size distributions in the submicrometer size range is the Scanning Mobility Particle Sizer (SMPS) including a Differential Mobility Analyzer (DMA) to select a narrow particle size followed by a Condensation Particle Counter (CPC) to count individual particles.



The Model 3563 Integrating Nephelometer is designed for long-term monitoring of visual range and air quality in ground-based and airborne studies. It continuously monitors the light scattering coefficient of airborne particles. Investigations have provided much evidence that particles present in the air (aerosols) are affecting the radiation reaching the earth’s surface.

This has direct implications on global warming and the increase of Global temperatures. Nephelometers measure light scattering and therefore is the perfect tool to study this aspect of global warming.



The CLAP is similar to the Radiance Research Particle Soot/Absorption Photometer (PSAP) in that it is a filter-based light absorption measurement. It differs from the PSAP in that it utilizes solenoid valves to cycle through 8 sample filter spots and 2 reference filter spots, enabling the instrument to run at ideal conditions (filter transmittance, Tr, greater than 0.7). The CLAP uses 47mm diameter, glass-fiber filters.



The CCN measures aerosol particles called cloud condensation nuclei that can form into cloud droplets. The instrument operates by supersaturating sample air to the point the where the CCN become detectable particles, which are then sized using an optical particle counter and distributed into 20 bins. The CCN operates by maintaining a positive temperature differential between the top of the column and the bottom. The top of the column always starts at ambient temperature or slightly above. For high supersaturations, temperature differentials of 20º C or more are required.

Microtops II Sun photometer


Sun photometers are specialized narrow field-of-view radiometers designed to measure solar irradiance. They typically have between 6 and 10 well-defined spectral bands, each of the order of 10nm full width at half maximum (FWHM). Sun photometer measurements can be used to recover atmospheric parameters including; spectral aerosol optical depth, precipitable water vapor, sky radiance distributions and ozone amount. Aerosol volume and size distribution are retrievable by inversion modelling from the spectral aerosol optical depth.


Fig. 1. Time series of daily mean values of the total column ozone content from MICROTOPS ozonometer during 2016-2019 in BEO Moussala

Gas Analyzer

NO2 NO NOx (AC32M “Environnement”)


Analyzer model AC32M chemiluminescence based analyzer capable of measuring nitrogen oxides at ppb levels. Applied to nitrogen oxides measurement, Chemiluminescence corresponds to an oxidation of NO molecules by O3 molecules. The return to a fundamental electronic state of the excited NO2 molecules is made by luminous radiation, detected by the PM tube.

CO2 (CO12M “Environnement”)


The analyzer was developed to meet customers’ requirement for reduced and easier maintenance. Equipped with sealed gas cells located in the airtight thermos regulated measurement module, the CO12M combines a powerful, easy-to-use interface with state-of-the-art components and design technology. The CO2 sample concentration is determined by measuring how much infrared light the sample gas absorbs as it flows through a multi-cell correlation wheel filled on one side with a reference CO2 cell (reference beam) and on the other side with an empty cell.

Piccaro G2301 Gas Concentration Analyser

Piccaro G2301 Gas Analyser

The Picarro G2301 gas concentration analyzer provides simultaneous, precise measurement of carbon dioxide (CO2), methane (CH4), and water (H2O) vapor at parts-per-billion (ppb) sensitivity with negligible drift for atmospheric science, air quality, and emissions quantification. It meets the World Meteorological Organization (WMO) and Integrated Carbon Observation System (ICOS) performance requirements for CO2 and CH4 atmospheric monitoring.

Patented Picarro cavity ring-down spectroscopy (CRDS) technology enables an effective measurement path length of up to 20 kilometers in a compact cavity,
which results in exceptional precision and sensitivity in a small-footprint analyzer.
CH4 Moussala
Fig. 2. Preliminary results of regional background concentrations of CH4 in BEO Moussala
CO2 Moussala
Fig. 3. Preliminary results of regional background concentrations of CO2 in BEO Moussala
CO2 Moussala
Fig. 4. Diurnal cycles of regional background concentrations of CO2 in BEO Moussala