Séminaire – Anthropogenic Pollution at a Remote Mountain Site in the western North Pacific

Stephen Griffith (National Taiwan University) 

Jeudi 20 Juillet à 14h00

Abstract :
Anthropogenic pollution, including long-range transported and local upslope pollution, are a threat to sensitive mountain ecosystems, which are already under continued threat of diminished area, due to climate change. Lulin Atmospheric Background Station (LABS; 2,862 meters asl) is a sub-tropical site in Taiwan and representative of a sensitive mountain ecosystem that is periodically enshrouded in fog and that receives long-range transported air masses from various clean and polluted origins and local pollution from mountain valley flows below. In this seminar, two narratives are followed: (i) clean vs. polluted days without fog at LABS and (ii) polluted foggy conditions. In the first story, clean and polluted days were characterized with spot sampling of VOCs, including a limited set of carbonyls, routine measurements, including ozone, CO, and PM_2.5, and reanalysis data, including NOx and HNO₃ concentrations, which were then all incorporated into an oxidant modeling analysis. Back-trajectories indicated different air masses influenced these two days, which was supported by distinctly different pollutant concentrations and subsequently calculated OH reactivity values. From the 0-dimensional modeling analysis, the first day was simulated to have a higher level of ozone production, but the second day also captured an afternoon spike in pollutants and ozone production that was likely driven by upslope mountain valley air sourced from lower altitudes in Taiwan. Thus, the oxidation potential in this environment is characterized by large swings driven by the shifting of air masses arriving at the site. The second story focused on cloud scavenging and processing of polluted air masses, which alter the fog composition and could have important implications for wet deposition to this environment. Inorganic concentrations and organic acid, sugar, and humic-like substances (HULIS) concentrations were all included in the analysis. Air masses arriving from Southeast Asia were associated with twice higher organic loadings, but a higher pH and were likely less impacted by cloud processing en route than air masses arriving from South China; thus highlighting the possible impacts of cloud processing on this sensitive environment.