Correction for “Global airborne sampling reveals a previously unobserved dimethyl sulfide oxidation mechanism in the marine atmosphere,” by Patrick R. Veres, J. Andrew Neuman, Timothy H. Bertram, Emmanuel Assaf, Glenn M. Wolfe, Christina J. Williamson, Bernadett Weinzierl, Simone Tilmes, Chelsea R. Thompson, Alexander B. Thames, Jason C. Schroder, Alfonso Saiz-Lopez, Andrew W. Rollins, James M. Roberts, Derek Price, Jeff Peischl, Benjamin A. Nault, Kristian H. Møller, David O. Miller, Simone Meinardi, Qinyi Li, Jean-François Lamarque, Agnieszka Kupc, Henrik G. Kjaergaard, Douglas Kinnison, Jose L. Jimenez, Christopher M. Jernigan, Rebecca S. Hornbrook, Alan Hills, Maximilian Dollner, Douglas A. Day, Carlos A. Cuevas, Pedro Campuzano-Jost, James Burkholder, T. Paul Bui, William H. Brune, Steven S. Brown, Charles A. Brock, Ilann Bourgeois, Donald R. Blake, Eric C. Apel, and Thomas B. Ryerson, which was first published February 18, 2020; 10.1073/pnas.1919344117 (Proc. Natl. Acad. Sci. U.S.A. 117, 4505–4510). The authors note that “hydroperoxymethyl thioformate (HPMTF) mixing ratios have been reduced, based upon recent experimental work that has identified a correction to the calibration method used to determine the instrument sensitivity for HPMTF measurements during ATom-3 and ATom-4. In the original calibration procedure, described in SI Appendix, section 1, HPMTF was produced using Cl• radical reaction with dimethyl sulfide (DMS). The measured change in Cl2 was used to determine HPMTF production; however, a contaminant yielded an overestimation in the measured Cl• radical concentration. More recent and more accurate actinometry of the produced Cl radicals has shown that instrument sensitivity to HPMTF was underestimated in these initial experiments. “HPMTF mixing ratios published in this manuscript are corrected by applying a project average scaling factor of 0.62 ± 0.11 (1 s) to the observations. The publicly available dataset has been updated through the Distributed Active Archive Center for Biogeochemical Dynamics (1). The HPMTF uncertainties have also been updated and are now reported for 1-s data to be 17% + 0.3 ppt accuracy and 0.4 ppt precision for ATom-3 and 12% + 0.4 ppt accuracy and 0.3 ppt precision for ATom-4.” As a result of this change, Figs. 1–4 have been updated. The corrected figures and their legends appear below. Also as a result of this change, the authors note that some text in the main article and SI Appendix should be corrected. On page 4506, right column, first paragraph, line 6, “Detection limits were better than 1 parts per trillion as a mole fraction in dry air (ppt), with an uncertainty of 55% + 0.06 ppt and a precision of 0.1 ppt for 1-s measurements (details in SI Appendix)” should instead appear as “Detection limits were better than 1 parts per trillion as a mole fraction in dry air (ppt), with an uncertainty of 17% + 0.4 ppt and a precision of 0.4 ppt for 1-s measurements (details in SI Appendix).” On the same page, right column, first full paragraph, line 8, “HPMTF is globally ubiquitous in the lower atmosphere over both seasons sampled, with MBL mixing ratios frequently exceeding 50 ppt and periodically as large as several hundred ppt (Fig. 2)” should instead appear as “HPMTF is globally ubiquitous in the lower atmosphere over both seasons sampled, with MBL mixing ratios frequently exceeding 10 ppt and periodically as large as 100 ppt (Fig. 2).” Also on the same page, right column, second full paragraph, line 6, “HPMTF was typically observed in a 1:1 ratio with DMS in the MBL; however, values in excess of 2:1 were frequently encountered. For example, the largest HPMTF mixing ratios of more than 300 ppt were observed over the South Atlantic Ocean (46°S and 53°W) during ATom-3” should instead appear as “HPMTF was typically observed in a 0.5:1 ratio with DMS in the MBL; however, values in excess of 1:1 were periodically encountered. For example, the largest HPMTF mixing ratios of more than 150 ppt were observed over the South Atlantic Ocean (46°S and 53°W) during ATom-3.” In the SI Appendix, the authors note that “we originally stated that ‘Cl2 quantification is possible using the iodide CIMS instrumentation (6) allowing for the determination of Cl• concentration following photolysis’ and later stated ‘Under these conditions we assume that the concentration of HPMTF produced is equivalent to twice the measured concentration of Cl2 lost via photolysis.’ In the updated calibration procedure, the change in Cl2, from photolytic loss and subsequent reaction with DMS, is below the detection limit of the instrument. For quantification of Cl• concentration we utilize a more accurate actinometry of chlorine radicals.” Panel A of Fig. S8 has been removed. Therefore, the following statement is no longer applicable: “Fig. S8A shows an example of a calibration experiment where loss of Cl2 is accompanied by an increase in HPMTF during photolysis.” These sentences have been omitted in the updated SI Appendix. On page 4, second full paragraph, line 1, “An absolute sensitivity of 2.4 ± 1.2 Hz ppt-1 was determined for the detection of HPMTF using iodide-adduct TOF CIMS in ATom. This sensitivity is about 5x less than the most sensitive compounds (e.g. Cl2, ClNO2, N2O5) and similar to that for BrO” should instead appear as “The average normalized instrument sensitivity to the detection of HPMTF using iodide-adduct TOF CIMS was 9.0 ± 3.2 (1σ) Hz ppt-1, normalized to 1 MHz IH2O− averaged across ATom-3 and ATom-4. This sensitivity is similar to the most sensitive compounds (e.g. Cl2, ClNO2, N2O5).” In addition, the following changes have been made to the SI Appendix reference list: The authors note that ref. 6 “was used to establish the mass spectrometer as a quantitative method for Cl2 measurement. The updated calibration procedure no longer utilizes the observed change in Cl2 as a method for quantification of Cl radicals (Cl•) production; therefore, the reference is no longer relevant to the manuscript.” Ref. 6 has been removed. Citations for refs. 57–59 were out of order and appeared earlier in the SI than indicated. The citations have been renumbered and refs. 57–59 now appear as references 19–21. Furthermore, refs. 50 and 61 were duplicated and have now been combined into a single ref. 52. The SI Appendix reference list has been renumbered to reflect these changes. Lastly, Figs. S1, S2, S5, and S8 are also affected by the correction to HPMTF data. The legend for Fig. S8 has been updated to reflect the changes. The online version has been updated to include the corrected text described above, the corrected Figs. 1–4, and the corrected SI Appendix.
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