In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 21, No. 13 ( 2021-07-06), p. 10111-10132
Abstract:
Abstract. Volatile organic compounds (VOCs) are ubiquitous in the atmosphere and are
important for atmospheric chemistry. Large uncertainties remain in the role
of the ocean in the atmospheric VOC budget because of poorly constrained
marine sources and sinks. There are very few direct measurements of air–sea
VOC fluxes near the coast, where natural marine emissions could influence
coastal air quality (i.e. ozone, aerosols) and terrestrial gaseous emissions
could be taken up by the coastal seas. To address this, we present air–sea flux measurements of acetone,
acetaldehyde and dimethylsulfide (DMS) at the coastal Penlee Point
Atmospheric Observatory (PPAO) in the south-west UK during the spring
(April–May 2018). Fluxes of these gases were measured simultaneously by eddy
covariance (EC) using a proton-transfer-reaction quadrupole mass
spectrometer. Comparisons are made between two wind sectors representative
of different air–water exchange regimes: the open-water sector facing the
North Atlantic Ocean and the terrestrially influenced Plymouth Sound fed by
two estuaries. Mean EC (± 1 standard error) fluxes of acetone, acetaldehyde and DMS
from the open-water wind sector were −8.0 ± 0.8, −1.6 ± 1.4
and 4.7 ± 0.6 µmol m−2 d−1 respectively (“−” sign
indicates net air-to-sea deposition). These measurements are generally
comparable (same order of magnitude) to previous measurements in the eastern North Atlantic Ocean at the same latitude. In comparison, the Plymouth Sound
wind sector showed respective fluxes of −12.9 ± 1.4, −4.5 ± 1.7
and 1.8 ± 0.8 µmol m−2 d−1. The greater deposition
fluxes of acetone and acetaldehyde within the Plymouth Sound were likely to
a large degree driven by higher atmospheric concentrations from the
terrestrial wind sector. The reduced DMS emission from the Plymouth Sound
was caused by a combination of lower wind speed and likely lower dissolved
concentrations as a result of the estuarine influence (i.e. dilution). In addition, we measured the near-surface seawater concentrations of
acetone, acetaldehyde, DMS and isoprene from a marine station 6 km offshore.
Comparisons are made between EC fluxes from the open-water and bulk air–sea
VOC fluxes calculated using air and water concentrations with a two-layer (TL)
model of gas transfer. The calculated TL fluxes agree with the EC
measurements with respect to the directions and magnitudes of fluxes,
implying that any recently proposed surface emissions of acetone and
acetaldehyde would be within the propagated uncertainty of 2.6 µmol m−2 d−1. The computed transfer velocities of DMS, acetone and acetaldehyde
from the EC fluxes and air and water concentrations are largely consistent with
previous transfer velocity estimates from the open ocean. This suggests that
wind, rather than bottom-driven turbulence and current velocity, is the main
driver for gas exchange within the open-water sector at PPAO (depth of
∼ 20 m).
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-21-10111-2021
DOI:
10.5194/acp-21-10111-2021-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2021
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
Permalink
