Trans-Himalayan Transport of Organochlorine Compounds: Three-Year Observations and Model-Based Flux Estimation

Area of Science:

• Environmental Chemistry
• Atmospheric Science
• Geochemistry

Background:

• High mountains act as barriers to atmospheric pollutant dispersion.
• Semivolatile chemicals, including persistent organic pollutants (POPs), can accumulate in mountainous regions.
• Mechanisms of POPs transport over major mountain ranges remain incompletely understood.

Purpose of the Study:

• To investigate the transport processes of persistent organic pollutants (POPs) across the central Himalayas.
• To quantify POPs transport facilitated by deep convection and mountain valleys.
• To determine the dominant pathways for POPs movement over high-altitude barriers.

Main Methods:

• A three-year atmospheric sampling campaign along a south-north altitudinal transect (100-5200m) in the Himalayas.
• Application of a multicompartment contaminant fate model to simulate POPs transport.
• Analysis of POPs deposition, scavenging, and cross-mountain fluxes.

Main Results:

• POPs emitted in Himalayan lowlands can reach high altitudes and the Tibetan Plateau.
• Over 90% of POPs are removed via deposition and scavenging during transport.
• An estimated 2 × 10^-3 to 1 × 10^-1 Gg/year of POPs are transported across the Himalayas.
• Valley transport flux is 2-3 times higher than ridge transport, but limited by spatial coverage.

Conclusions:

• POPs can overcome the Himalayan blocking effect, with high-altitude transport being the dominant pathway.
• Atmospheric transport of POPs across mountain ranges is significant.
• Understanding these transport dynamics is crucial for regional and global pollution assessments.