response to the comments

Abstract

Due to their properties of bioaccumulation, toxicity, and long-range atmospheric transport, polyfluoroalkyl and perfluoroalkyl substances (PFASs) and cyclic volatile methylsiloxanes (cVMSs) are currently being considered as emerging persistent organic pollutants (POPs) for regulation. To date, there are limited data on PFASs and cVMSs in the atmosphere of the Tibetan Plateau (TP), a remote environment which can provide information on global background conditions. Sorbent-impregnated polyurethane foam (SIP) disc passive air samplers were therefore deployed for 3 months (May to July 2011 and 2013) at 16 locations across the TP. Using previously reported methods for estimating the air volume sampled by SIP discs, the derived atmospheric concentrations ranged as follows: 18-565 ng m −3 for cVMS (including D3, D4, D5, and D6); 65-223 pg m −3 for fluorotelomer alcohols ( FTOHs); 1.2-12.8 pg m −3 for fluorinated sulfonamides ( FOSA); and 0.29-1.02 pg m −3 for fluorinated sulfonamidoethanols ( FOSE). The highest cVMS occurred at Lhasa, the capital city of the TP, indicating the local contribution to the emerging pollutants. Higher levels of FTOHs were observed at sites close to the transport channel of the Yarlung Tsangpo Grand Canyon, indicating possible long-range atmospheric transport (LRAT). Elevated concentrations of shorter-chain volatile PFAS precursors (4 : 2 FTOH and fluorobutane sulfonamidoethanol) were found in most air samples, reflecting the shift in production from long-to short-chain PFASs in Asia. Overall, concentrations of emerging POPs at background sites of the TP were 1-3 orders of magnitude higher than those reported for legacy POPs.