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On the Transport of Urban Pollution in an Andean Mountain Valley

Category: Regional Air Pollution

Volume: 16 | Issue: 3 | Pages: 593-605
DOI: 10.4209/aaqr.2015.05.0371
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Ana María Cordova1, Jorge Arévalo1, Julio C. Marín 1, Darrel Baumgardner2, Graciela B. Raga3, Diana Pozo1, Carlos A. Ochoa3, Roberto Rondanelli4,5

  • 1 Departamento de Meteorología, Universidad de Valparaíso, (null), Chile
  • 2 Droplet Measurements Technology, (null), USA
  • 3 Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, (null), Mexico
  • 4 Departamento de Geofísica, Universidad de Chile, (null), Chile
  • 5 Center for Climate and Resilience Research, Santiago, Chile

Highlights

A 5-week PISCES campaign was carried out in the Chilean Andes, SE of Santiago.
Clear diurnal cycle of CN concentrations on clear days, not present on cloudy days.
Evidence of up-valley/upslope flow during the afternoon driven by surface heating.
No day-night wind reversal on cloudy days due to reduced surface forcing.
No evidence at the site of polluted PBL air from Santiago, from back trajectories.


Abstract

Urban pollution can often impact surrounding, non-urban regions, through advection and dispersal of pollutants by the prevailing winds. Urban regions located upstream of high mountains, such as the Andes, can potentially impact the cryosphere by deposition of particles onto the surface of the snowpack and glaciers.

Santiago, the capital of Chile, has more than 6 million inhabitants and regularly experiences episodes of severe pollution, particularly during the austral winter. Some studies have hypothesized that particle pollution from Santiago can reach the cryosphere downwind of the city, but the scarcity of measurements made high in the mountains prevents the validation of mesoscale models so the proof of actual impact remains elusive. A research project was designed to provide some insight into this question. The Pollution Impact on Snow in the Cordillera - Experiments and Simulations (PISCES) project was carried out in 2014 and includes both observational and modeling components. A five-week field campaign was conducted at the end of winter, at an elevated site in a mountain valley, 65 km to the southeast of the center of Santiago, to characterize some aspects of particulate pollution.

During synoptic conditions that result in clear days at the site, the mesoscale mountain-valley circulation is effective in transporting pollutants upwards during the day, leading to diluted particle concentrations beyond the summits of the highest peaks. Cloudy days with reduced up-valley circulation do not show increased concentrations associated with transport. Back trajectories indicate that airmasses reaching the site during the field campaign are seldom influenced by pollution from Santiago.

Keywords

Andes cryosphere Black carbon Regional pollution Mountain-valley circulations


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