A monitoring programme for halogenated climate-altering gases has been established in the frame of the SHARE EV-K2 -CNR project at the Nepal Climate Laboratory – Pyramid in the Himalayan range at the altitude of 5079 m a.s.l. The site is very well located to provide important insights on changes in atmospheric composition in a region that is of great significance for emissions of both anthropogenic and biogenic halogenated compounds. Measurements are performed since March 2006, with grab samples collected on a weekly basis. The first three years of data have been analysed. After the identification of the atmospheric background values for fourteen halocarbons, the frequency of occurrence of pollution events have been compared with the same kind of analysis for data collected at other global background stations. The analysis showed the fully halogenated species, whose production and consumption are regulated under the Montreal Protocol, show a significant occurrence of “above the baseline” values, as a consequence of their current use in the developing countries surrounding the region, meanwhile the hydrogenated gases, more recently introduced into the market, show less frequent spikes. Atmospheric concentration trends have been calculated as well, and they showed a fast increase, ranging from 5.7 to 12.6%, of all the hydrogenated species, and a clear decrease of methyl chloroform(-17.7%).The comparison with time series from other stations has also allowed to derive Meridional gradients, which are absent for long living well mixed species, while for the more reactive species, the gradient in creases inversely with respect to their atmospheric lifetime. The effect of long range transport and of local events on the atmospheric composition at the station has been analysed as well, allowing the identification of relevant source regions the Northern half of the Indian sub-continent. Also, at finer spatial scales, a smaller, local contribution of forest fires from the Khumbu valley has been detected.

In the framework of the SusKat (Sustainable Atmosphere for the Kathmandu Valley), ABC-UNEP and NextData Projects, CNR-ISAC and URT Ev-K2-CNR participated in the setting-up of the Kathmandu (Pakanajol) monitoring station. In particular, the station is equipped with: • meteorological sensors; • global pyranometer for downward solar short-wave radiation; • surface ozone analyzer; • optical particle counter for aerosol size distribution from 0.3 to 10 micron; • on-line PM1/PM10 analyser ; • multi-angle absorption photometer for equivalent black carbon mass measurement.

In the framework of the SusKat (Sustainable Atmosphere for the Kathmandu Valley), ABC-UNEP and NextData Projects, CNR-ISAC and URT Ev-K2-CNR participated in the setting-up of the Kathmandu (Pakanajol) monitoring station. In particular, the station is equipped with: • meteorological sensors; • global pyranometer for downward solar short-wave radiation; • surface ozone analyzer; • optical particle counter for aerosol size distribution from 0.3 to 10 micron; • on-line PM1/PM10 analyser ; • multi-angle absorption photometer for equivalent black carbon mass measurement.

In the framework of the SusKat (Sustainable Atmosphere for the Kathmandu Valley), ABC-UNEP and NextData Projects, CNR-ISAC and URT Ev-K2-CNR participated in the setting-up of the Kathmandu (Pakanajol) monitoring station. In particular, the station is equipped with: • meteorological sensors; • global pyranometer for downward solar short-wave radiation; • surface ozone analyzer; • optical particle counter for aerosol size distribution from 0.3 to 10 micron; • on-line PM1/PM10 analyser ; • multi-angle absorption photometer for equivalent black carbon mass measurement.

In the framework of the SusKat (Sustainable Atmosphere for the Kathmandu Valley), ABC-UNEP and NextData Projects, CNR-ISAC and URT Ev-K2-CNR participated in the setting-up of the Kathmandu (Pakanajol) monitoring station. In particular, the station is equipped with: • meteorological sensors; • global pyranometer for downward solar short-wave radiation; • surface ozone analyzer; • optical particle counter for aerosol size distribution from 0.3 to 10 micron; • on-line PM1/PM10 analyser ; • multi-angle absorption photometer for equivalent black carbon mass measurement.

In the framework of the SusKat (Sustainable Atmosphere for the Kathmandu Valley), ABC-UNEP, SHARE and NextData Projects, CNR-ISAC and URT Ev-K2-CNR participated in the setting-up of the Kathmandu (Pakanajol) monitoring station. In particular, the station is equipped with: • meteorological sensors; • global pyranometer for downward solar short-wave radiation; • surface ozone analyzer; • optical particle counter for aerosol size distribution from 0.3 to 10 micron; • on-line PM1/PM10 analyser ; • multi-angle absorption photometer for equivalent black carbon mass measurement.

This paper provides a detailed description of the atmospheric conditions characterizing the high Himalayas, thanks to continuous observations begun in March 2006 at the Nepal Climate Observatory-Pyramid (NCO-P) located at 5079 m a.s.l. on the southern foothills of Mt. Everest, in the framework of ABC UNEP and SHARE-Ev-K2-CNR projects. The work presents a characterization of meteorological conditions and air-mass circulation at NCO-P during the first two years of activity.The mean values of atmospheric pressure, temperature and wind speed recorded at the site were: 551 hPa, -3.0°C, 4.7 m s -1 ,respectively. The highest seasonal values of temperature (1.7 ° C) and relative humidity (94%) were registered during the monsoon season, which was also characterized by thick clouds, present in about 80% of the afternoon hours, and by a frequency of cloud-free sky of less than 10%. The lowest temperature and relative humidity seasonal values were registered during winter, -6.3°C and 22%, respectively, the season being characterised by mainly cloud-free sky conditions and rarehick clouds. The summer monsoon influenced rain precipitation (seasonal mean: 237 mm), while wind was dominated by flows from the bottom of the valley (S-SW) and upper mountain (N-NE).The atmospheric composition at NCO-P has been studied thanks to measurements of black carbon (BC),aerosol scattering coefficient, PM1, coarse particles and ozone The annual behaviour of the measured parameters shows the highest seasonal values during the premonsoon (BC: 316.9 ng m-3,PM1: 3.9 µg m-3, scattering coeffcient: 11.9 Mm-1 , coarse particles: 0.37 cm-3 and O3: 60.9 ppbv), while the lowest concentrations occurred during the monsoon (BC: 49.6 ng m-3, PM1: 0.6 µg m-3 , scattering coefficient: 2.2 Mm-1 , and O3: 38.9 ppbv) and, for coarse particles, during the post-monsoon (0.07 cm-3 ). At NCO-P, the synoptic-scale circulation regimes present three principal contributions: Westerly, South Westerly and Regional, as shown by the analysis of in-situ meteorological parameters and 5-day LAGRANTO back trajectories. The influence of the brown cloud (AOD>0.4) extending over Indo Gangetic Plains up to the Himalayan foothills has been evaluated by analysing the in-situ concentrations of the ABC constituents. This analysis revealed that brown cloud hot spots mainly influence the South Himalayas during the pre monsoon, in the presence of very high levels of atmospheric compounds (BC: 1974.1 ng m-3 , PM1: 23.5 µg m-3,scattering coefficient: 57.7 Mm-1,coarse particles: 0.64 cm-3, O3: 69.2 ppbv, respectively). During this season 20% of the days were characterised by a strong brown cloud influence during the afternoon, leading to a 5-fold increased in the BC and PM1 values, in comparison with seasonal means. Our investigations provide clear evidence that, especially during the pre-monsoon, the southern side of the high Himalayan valleys represent a “direct channel” able to transport brown cloud pollutants up to 5000 m a.s.l., where the pristine atmospheric composition can be strongly influenced.

This paper provides a detailed description of the atmospheric conditions characterizing the high Himalayas, thanks to continuous observations begun in March 2006 at the Nepal Climate Observatory-Pyramid (NCO-P) located at 5079 m a.s.l. on the southern foothills of Mt. Everest, in the framework of ABC UNEP and SHARE-Ev-K2-CNR projects. The work presents a characterization of meteorological conditions and air-mass circulation at NCO-P during the first two years of activity.The mean values of atmospheric pressure, temperature and wind speed recorded at the site were: 551 hPa, -3.0°C, 4.7 m s -1 ,respectively. The highest seasonal values of temperature (1.7 ° C) and relative humidity (94%) were registered during the monsoon season, which was also characterized by thick clouds, present in about 80% of the afternoon hours, and by a frequency of cloud-free sky of less than 10%. The lowest temperature and relative humidity seasonal values were registered during winter, -6.3° C and 22%, respectively, the season being characterised by mainly cloud-free sky conditions and rarehick clouds. The summer monsoon influenced rain precipitation (seasonal mean: 237 mm), while wind was dominated by flows from the bottom of the valley (S-SW) and upper mountain (N-NE). The atmospheric composition at NCO-P has been studied thanks to measurements of black carbon (BC), aerosol scattering coefficient, PM1, coarse particles and ozone.The annual behaviour of the measured parameters shows the highest seasonal values during the premonsoon (BC: 316.9 ng m-3 , PM1: 3.9 µg m-3, scattering coefficient: 11.9 Mm-1 , coarse particles: 0.37 cm-3 and O3: 60.9 ppbv), while the lowest concentrations occurred during the monsoon (BC: 49.6 ng m-3 , PM1: 0.6 µg m-3 , scattering coefficient: 2.2 Mm-1 , and O3: 38.9 ppbv) and, for coarse particles, during the post-monsoon (0.07 cm-3 ). At NCO-P, the synoptic-scale circulation regimes present three principal contributions: Westerly, South-Westerly and Regional, as shown by the analysis of in-situ meteorological parameters and 5-day LAGRANTO back-trajectories. The influence of the brown cloud (AOD>0.4) extending over Indo–Gangetic Plains up to the Himalayan foothills has been evaluated by analysing the in-situ concentrations of the ABC constituents. This analysis revealed that brown cloud hot spots mainly influence the South Himalayas during the pre-monsoon, in the presence of very high levels of atmospheric compounds (BC: 1974.1 ng m-3 , PM1: 23.5 µg m-3, scattering coefficient: 57.7 Mm-1, coarse particles: 0.64 cm-3, O3: 69.2 ppbv, respectively). During this season 20% of the days were characterised by a strong brown cloud influence during the afternoon, leading to a 5-fold increased in the BC and PM1 values, in comparison with seasonal means. Our investigations provide clear evidence that, especially during the pre-monsoon, the southern side of the high Himalayan valleys represent a “direct channel” able to transport brown cloud pollutants up to 5000 m a.s.l., where the pristine atmospheric composition can be strongly influenced.

The paper presents the first 2-years of continuous surface ozone (O3) observations and systematic assessment of the influence of stratospheric intrusions (SI) at the Nepal Climate Observatory at Pyramid (NCO-P; 27°57' N, 86°48' E), located in the Southern Himalayas at 5079 m a.s.l. Continuous O3 monitoring has been carried out at this GAW-WMO station in the framework of the Ev-K2-CNR SHARE and UNEP ABC projects since March 2006. Over the period March 2006–February 2008, an average O3 value of 49±12 ppbv (±1?) was recorded, with a large annual cycle characterized by a maximum during the pre-monsoon (61±9 ppbv) and a minimum during the monsoon (39±10 ppbv). In general, the average O3 diurnal cycles had different shapes in the different seasons, suggesting an important interaction between the synoptic-scale circulation and the local mountain wind regime. Short-term O3 behaviour in the middle/lower troposphere (e.g. at the altitude level of NCO-P) can be significantly affected by deep SI which, representing the most important natural input for tropospheric O3, can also influence the regional atmosphere radiative forcing. To identify days possibly influenced by SI at the NCO-P, analyses were performed on in-situ observations (O3 and meteorological parameters), total column O3 data from OMI satellite and air-mass potential vorticity provided by the LAGRANTO back-trajectory model. In particular, a specially designed statistical methodology was applied to the time series of the observed and modelled stratospheric tracers. On this basis, during the 2-year investigation, 14.1% of analysed days were found to be affected by SI. The SI frequency showed a clear seasonal cycle, with minimum during the summer monsoon (1.2%) and higher values during the rest of the year (21.5%). As suggested by the LAGRANTO analysis, the position of the subtropical jet stream could play an important role in determining the occurrence of deep SI transport on the Southern Himalayas. In order to estimate the fraction of O3 due to air-mass transport from the stratosphere at the NCO-P, the 30 min O3 concentrations recorded during the detected SI days were analysed. In particular, in-situ relative humidity and black carbon observations were used to exclude influence from wet and polluted air-masses transported by up-valley breezes. This analysis led to the conclusion that during SI O3 significantly increased by 27.1% (+13 ppbv) with respect to periods not affected by such events. Moreover, the integral contribution of SI (O3S) to O3 at the NCO-P was also calculated, showing that 13.7% of O3 recorded at the measurement site could be attributed to SI. On a seasonal basis, the lowest SI contributions were found during the summer monsoon (less than 0.1%), while the highest were found during the winter period (24.2%). These results indicated that, during non-monsoon periods, high O3 levels could affect NCO-P during SI, thus influencing the variability of tropospheric O3 over the Southern Himalayas. Being a powerful regional greenhouse gas, these results indicate that the evaluation of the current and future regional climate cannot be assessed without properly taking into account the influence of SI to tropospheric O3 in this important area.

In the framework of the SusKat (Sustainable Atmosphere for the Kathmandu Valley), ABC-UNEP and NextData Projects, CNR-ISAC and URT Ev-K2-CNR participated in the setting-up of the Kathmandu (Pakanajol) monitoring station. In particular, the station is equipped with: • meteorological sensors; • global pyranometer for downward solar short-wave radiation; • surface ozone analyzer; • optical particle counter for aerosol size distribution from 0.3 to 10 micron; • on-line PM1/PM10 analyser ; • multi-angle absorption photometer for equivalent black carbon mass measurement.