In this work we present the new ABC-Pyramid Atmospheric Research Observatory (Nepal, 27.95 N, 86.82 E) located in the Himalayas, specifically in the Khumbu valley at 5079 m a.s.l. This measurement station has been set-up with the aim of investigating natural and human-induced environmental changes at different scales (local, regional and global). After an accurate instrumental set-up at ISAC-CNR in Bologna (Italy) in autumn 2005, the ABC-Pyramid Observatory for aerosol (physical, chemical and optical properties) and trace gas measurements (ozone and climate altering halocarbons) was installed in the high Khumbu valley in February 2006. Since March 2006, continuous measurements of aerosol particles (optical and physical properties), ozone (O3) and meteorological parameters as well as weekly samplings of particulate matter (for chemical analyses) and grab air samples for the determination of 27 halocarbons, have been carried out. These measurements provide data on the typical atmospheric composition of the Himalayan area between India and China and make investigations of the principal differences and similarities between the monsoon and pre-monsoon seasons possible. The study is carried out within the framework of the Ev-K2-CNR “SHARE-Asia” (Stations at High Altitude for Research on the Environment in Asia) and UNEP—“ABC” (Atmospheric Brown Clouds) projects. With the name of “Nepal Climate Observatory—Pyramid” the station is now part of the Observatory program of the ABC project.

The Himalayan–Karakoram range is located in one of the most densely populated and very rapidly developing world areas. Monitoring of atmospheric composition in this area can play a relevant role in evaluating the background conditions of the free troposphere and quantifying the pollution present at high altitudes, as well as in studying regional and long-range transport phenomena. Due to technical and logistic difficulties in carrying out measurements at high altitude in the Himalaya, no systematic observations of atmospheric constituents are available for this area. Thus, a new measurement station in such a region represents a unique source of data, able to make up for the prior lack of this information. For these reasons, in the framework of the SHARE-Asia and ABC projects, a remote monitoring station, the ABC-Pyramid Laboratory, will be installed in the Khumbu valley near Mt. Everst at 5079 m a.s.l. Continuous in situ measurements of chemical, physical and optical properties of aerosol, surface ozone concentration, as well as non-continuous measurements of halocarbons and other greenhouse-gas concentrations will be carried out. This monitoring station was projected, realised and tested in Bologna at CNR-ISAC Institute during autumn 2005. It was designed to be controlled by remote login and to operate for the long-term in extremely adverse weather conditions. This station represents an ideal place for studying regional and long-range air mass transport, due to natural and human processes. Precious 5-day forecast information about air-masses circulation at the ABC-Pyramid site will be supplied daily by Lagrangian backward trajectories, including suitable forecasts of stratosphere-troposphere exchange phenomena.

Absorption photometers for real time application have been available since the 1980s, but the use of filter-based instruments to derive information on aerosol properties (absorption coefficient and black carbon, BC) is still a matter of debate. Several workshops have been conducted to investigate the performance of individual instruments over the intervening years. Two workshops with large sets of aerosol absorption photometers were conducted in 2005 and 2007. The data from these instruments were corrected using existing methods before further analysis. The inter-comparison shows a large variation between the responses to absorbing aerosol particles for different types of instruments. The unit to unit variability between instruments can be up to 30% for Particle Soot Absorption Photometers (PSAPs) and Aethalometers. Multi Angle Absorption Photometers (MAAPs) showed a variability of less than 5%. Reasons for the high variability were identified to be variations in sample flow and spot size. It was observed that different flow rates influence system performance with respect to response to absorption and instrumental noise. Measurements with non absorbing particles showed that the current corrections of a cross sensitivity to particle scattering are not sufficient. Remaining cross sensitivities were found to be a function of the total particle load on the filter. The large variation between the response to absorbing aerosol particles for different types of instruments indicates that current correction functions for absorption photometers are not adequate.