14 Nov 2023
 | 14 Nov 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Shipping and algae emissions have a major impact on ambient air mixing ratios of NMHCs and methanethiol on Utö island in the Baltic Sea

Heidi Hellén, Rostislav Kouznetsov, Kaisa Kraft, Jukka Seppälä, Mika Vestenius, Jukka-Pekka Jalkanen, Lauri Laakso, and Hannele Hakola

Abstract. Mixing ratios of highly volatile organic compounds were studied on Utö Island in the Baltic Sea. Measurements of non-methane hydrocarbons (NMHCs) and methanethiol were conducted using an in situ thermal desorption-gas chromatograph-flame ionization detector/mass spectrometer (TD-GC-FID/MS) from March 2018 until March 2019. The mean mixing ratios of NMHCs (alkanes, alkenes, alkynes, aromatic hydrocarbons) were at the typical levels for rural/remote sites in Europe and as expected the highest mixing ratios were measured in winter while in summertime, the mixing ratios remained close to or below detection limits for most of the studied compounds. Sources of NMHCs during wintertime were studied using positive matrix factorization (PMF) together with wind direction analyses and source area estimates. Shipping was found to be a major local anthropogenic source of NMHCs with a 21 % contribution. It contributed especially on ethene, propene and ethyne mixing ratios. Other identified sources were gasoline fuel (15 %), traffic exhaust (14 %), local solvents (6 %), and long-range transported background (42 %). Contrary to NMHCs, high mixing ratios of methanethiol were detected in summertime (July mean 1000 pptv). The mixing ratios followed the variations of seawater temperatures and sea level height and were highest during the daytime. Biogenic phytoplankton or macroalgae emissions were expected to be the main source for methanethiol. 

Heidi Hellén et al.

Status: open (until 26 Dec 2023)

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Heidi Hellén et al.

Heidi Hellén et al.


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Short summary
Mixing ratios of C2-C5 NMHCs and methanethiol were measured on an island in Baltic Sea using an in-situ gas chromatograph. Shipping emissions were found to be an important source of ethene, ethyne, propene and benzene. High summertime mixing ratios of methanethiol and dependence of mixing ratios on sea water temperature and height indicated the biogenic origin possibly from phytoplankton or macroalgae. These emissions may have strong impacts on SO2 production and new particle formation.