In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 19, No. 23 ( 2019-11-29), p. 14431-14453
Kurzfassung:
Abstract. Total hydroxyl radical (OH) reactivity measurements were conducted at the second Station for Measuring
Ecosystem–Atmosphere Relations (SMEAR II), a boreal forest site located in Hyytiälä, Finland, from April
to July 2016.
The measured values were compared with OH reactivity calculated from a combination of data from the
routine trace gas measurements (station mast) as well as online and offline analysis with a gas chromatographer
coupled to a mass spectrometer (GC–MS) and offline liquid chromatography.
Up to 104 compounds, mostly volatile organic compounds (VOCs) and oxidized VOCs, but also inorganic compounds,
were included in the analysis, even though the data availability for each compound varied with time.
The monthly averaged experimental total OH reactivity was found to be higher in April and May (ca. 20 s−1)
than in June and July (7.6 and 15.4 s−1, respectively). The measured values varied much more in spring with
high reactivity peaks in late afternoon, with values higher than in the summer, in particular when the soil was
thawing.
Total OH reactivity values generally followed the pattern of mixing ratios due to change of the boundary layer
height.
The missing reactivity fraction (defined as the difference between measured and calculated OH reactivity) was
found to be high. Several reasons that can explain the missing reactivity are discussed in detail such
as (1) missing measurements due to technical issues, (2) not measuring oxidation compounds of detected
biogenic VOCs, and (3) missing important reactive compounds or classes of compounds with the available measurements.
In order to test the second hypothesis, a one-dimensional chemical transport model (SOSAA) has been used to
estimate the amount of unmeasured oxidation products and their expected contribution to the reactivity
for three different short periods in April, May, and July. However, only a small fraction
(〈4.5 %) of the missing reactivity can be explained by modelled secondary compounds (mostly oxidized VOCs).
These findings indicate that compounds measured but not included in the model as well as unmeasured primary
emissions contribute the missing reactivity. In the future, non-hydrocarbon compounds from sources other than
vegetation (e.g. soil) should be included in OH reactivity studies.
Materialart:
Online-Ressource
ISSN:
1680-7324
DOI:
10.5194/acp-19-14431-2019
DOI:
10.5194/acp-19-14431-2019-corrigendum
Sprache:
Englisch
Verlag:
Copernicus GmbH
Publikationsdatum:
2019
ZDB Id:
2092549-9
ZDB Id:
2069847-1
