Measurement Report: Long-range transport and fate of DMS-oxidation products in the free troposphere derived from observations at the high-altitude research station Chacaltaya (5240 m a.s.l.) in the Bolivian Andes

Dimethyl sulfide (DMS) is the primary natural contributor to the atmospheric sulfur burden. Observations concerning the fate of DMS oxidation products after long-range transport in the remote free troposphere are, however, sparse. Here we present quantitative chemical ionization mass spectrometric measurements of DMS and its oxidation products H2SO4, MSIA, MTF, CH3S(O)2OOH and CH3SOH in the gas-phase as well as measurements of the sulfate and methane- 5 sulfonate aerosol mass fractions at the Global Atmosphere Watch (GAW) station Chacaltaya in the Bolivian Andes located at above sea level (a.s.l.). observed next to reactive intermediates such as methyl thioformate, dimethyl sulfoxide, and methane sulfinic acid. Also for this event, backtrajectory calculations show, that the air masses came from above the ocean (distance >330 km) with no local sur- 15 face contacts. This study demonstrates the potential impact of marine DMS emissions on the availability of sulfur-containing vapors in the remote free troposphere far away from the ocean. The array of time-of-flight mass spectrometers using different ionization methods and the low limit of detection allowed for the quantification of DMS, dimethyl sulfoxide (DMSO), dimethyl sulfone ( DMSO 2 ), methane sulfinic acid (MSIA), methane sulfonic acid (MSA), and sulfuric acid in parallel. the long-term data set of particulate MSA indicates that the station is regularly influenced by air masses with marine origin. The effect of DMS oxidation on particle composition is nonetheless small it is competing with other of H 2 like 2 the region. it impossible to relate the MSA H 2 4 ratio oxidation previous measurements suggested DMS oxidation in the free troposphere, such a full spectrum of compounds from DMS oxidation as presented here has not been observed previously at such altitude and distance from sources, which provides insights into the fate of DMS in the free troposphere. Clearly, due to dilution and (wet) deposition losses, the concentrations of DMS oxidation products detected this far away from their sources are small. Our data suggest that their concentrations are too small to have an impact on new particle formation or growth directly at CHC, but - as previous results from flight campaigns have shown - particle formation and growth likely occur along the way while concentrations of MSA and DMS-derived sulfuric acid are still less diluted and the air masses are not impacted by volcanic emissions. To properly quantify the impact of DMS oxidation in the free troposphere, laboratory studies on particle formation rates with varying MSA and sulfuric acid concentrations and flight campaigns closer to marine updrafts with modern low-detection-limit proton transfer and nitrate cluster reaction mass spectrometers are needed in combination with physical and chemical aerosol characterization. the data of the spectrometers PTR3, nitrate-CIMS and Api-TOF, Q-ACSM, the FLEXPART lagrangian dispersion simulations and analysis; long term filter samples