Due to the covid-19 travel restrictions still on place worldwide, the annual steering committee meeting took place on-line on the 4th and 5th December 2020.

The next scientific meeting related to Chacaltaya GAW station will take place in La Paz, Bolivia between 22 and 24 June 2020.
Science advances and other topics will be discussed, the agenda will be disclosed in the forthcoming months.

This year, the Steering Committee Meeting took place between the 4th and 6th of June.
In this occasion we were honored by the presence of Lorenzo Labrador from the WMO and the president (Rector) of the University Mayor de San Andrés, Waldo Albarracín.
In the meeting, in addition to Chacaltaya current issues, some preliminary results intensive nucleation campagin SALTENA lead bt Federico Bianchi, were also discussed.
This year meeting was extremely intersting in terms of the science discussed and enriched by the presence of many special guests.

An intensive campaign aiming to understand the nucleation characteristics at CHC has started!

The goal of the campaign, led by Federico Bianchi, University of Helsinki,  is to further understand and quantify at a molecular level the various processes and mechanisms that govern new-particle formation in the free troposphere.

The 6-month field study with state-of-the-art instrumentation (APiTOFs, CI-APiTOFs, PTR3, PSMs, NAISs, etc) will complement the previous studies performed at Jungfraujoch (Switzerland) and Pyramid (Nepal) high altitude stations with similar setups.

From the comprehensive datasets, the scientific team expects to constrain the chemistry driving free-tropospheric new-particle formation and to answer the following questions:
- Are sulfuric acid concentrations high enough to enable nucleation on its own?
- Do ammonia or amines contribute to nucleation at this altitude far away from the sources?
- Can we observe pure organic nucleation?
- Are organosulfates or organonitrates essential contributors for new-particle formation?
- Are any organic compounds involved of biogenic or anthropogenic origin?
- What drives particle growth to 3 nm?

To answer theses questions, the project has three key scientific objectives:
- To determine the chemical nature of naturally  charged and neutral particles clusters at a
 high-altiude site complementary to the other  two previously studied sites; 
- To stablish a quantitative link between detected  clusters and newly formed particles; 
- To identify the impact of environmental conditions  on the cluster composition, by comparing results
 from fours different sites (Hyytiälä included) around the  world.

For more details, see the webpage of the Bolivia Campaign.

The annual meeting of the Chacaltaya Steering Committee was held on June the 5th and a visit to the station was scheduled for June the 7th in spite of the snowy conditions at Mount Chacaltya.

On June the 6th, some results of the complementary campaign La Paz Experiment were discussed. La Paz Experiment aims at characterizing the urban background emissions in La Paz and El Alto twin cities. These emissions are likely to affect the measurements in Chacaltaya.

After the meeting, some short seminars were held for the local students.

On August 31th, 2016, Valeria Mardóñez presented her bachelor memory about the atypical relationship between carbon monoxide (CO) and equivalent black carbon (eBC) concentrations in Chacaltaya.

Most of the time, CO and eBC are correlated in Chacaltaya, pointing at a vehicular origin of those emissions, but in several cases both pollutants are decoupled. 50 cases of the latter were studied together with meteorological variables, back trajectories, satellite images and hot spots derived from satellite data in order to find the reason of the decoupling.

Interestingly, the decoupling could be explained when different conditions were present: biomass burning, residual layer pollution (both regional and from the city nearby), high relative humidity, the transition between free troposphere and mixing layer and the change on wind speed and direction.  The relationship between those factors and the studied pollutants was not direct, but they could explain half of the studied cases.

As in some cases it was not possible to find a reason for the decoupling, more studies are needed.