Sunlight Induces the Production of Atmospheric Volatile Organic Compounds (VOCs) from Thermokarst Ponds

Abstract

Ground subsidence caused by permafrost thawing causes the formation of thermokarst ponds, where organic compounds from eroding permafrost accumulate. We photolyzed water samples from two such ponds in Northern Quebec and discovered the emission of volatile organic compounds (VOCs) using mass spectrometry. One pond near peat-covered permafrost mounds was organic-rich, while the other near sandy mounds was organic-poor. Compounds up to C10 were detected, comprising the atoms of O, N, and S. The main compounds were methanol, acetaldehyde, and acetone. Hourly VOC fluxes under actinic fluxes similar to local solar fluxes might reach up to 1.7 nmol C m–2 s–1. Unexpectedly, the fluxes of VOCs from the organic-poor pond were greater than those from the organic-rich pond. We suggest that different segregations of organics at the air/water interface may partly explain this observation. This study indicates that sunlit thermokarst ponds are a significant source of atmospheric VOCs, which may affect the environment and climate via ozone and aerosol formation. Further work is required for understanding the relationship between the pond’s organic composition and VOC emission fluxes.

Emission of Volatile Organic Compounds to the Atmosphere from Photochemistry in Thermokarst Ponds in Subarctic Canada

“…It was also 1 to 2 orders of magnitude lower than the VOCs fluxes from organic-rich soils in permafrost environments. In accordance with our earlier research, 37 we conclude that although VOCs represent a small contribution to C emissions from surface water to the atmosphere in the Arctic, sunlight-induced VOCs might disproportionally impact atmospheric chemistry and, possibly, the climate.…”

“…On the contrary, some of the dark-colored, DOC-rich ponds from SAS yielded fewer VOCs than the TAS ponds. Wang et al 37 reached similar results and proposed that optical properties of the water could provide explanatory insights, an assertion we develop in this work. The three proxies used, namely, a 320 , SUVA 254 , and Sr, give insights into the concentrations, aromatics, and molecular size of CDOM, respectively.…”

“…We have also tested the hypothesis that samples with higher CDOM content might lead to a wider variety and greater fluxes of photoproduced VOCs due to the observation that DOM photo lability is related to its chemical composition. 12,35,36 We build on our previous preliminary exploration 37 that demonstrated the feasibility of detecting VOCs from photolysis of natural pond water. Relying on a similar methodology, we have extended field sampling to four ponds, collecting samples at various depths, as well as riparian water.…”

“…We build on our previous preliminary exploration that demonstrated the feasibility of detecting VOCs from photolysis of natural pond water. Relying on a similar methodology, we have extended field sampling to four ponds, collecting samples at various depths, as well as riparian water.…”