Influence of anthropogenic emissions on the composition of highly oxygenated organic molecules in Helsinki: a street canyon and urban background station comparison
<p>Condensable vapors, including highly oxygenated organic molecules (HOMs), govern secondary organic aerosol formation and thereby impact the quantity, composition, and properties (e.g., toxicity) of aerosol particles. These vapors are mainly formed in the atmosphere through the oxidation of...
Main Authors: | , , , , , , , , , , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2023-10-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://acp.copernicus.org/articles/23/12965/2023/acp-23-12965-2023.pdf |
Summary: | <p>Condensable vapors, including highly oxygenated organic molecules
(HOMs), govern secondary organic aerosol formation and thereby impact the
quantity, composition, and properties (e.g., toxicity) of aerosol particles.
These vapors are mainly formed in the atmosphere through the oxidation of
volatile organic compounds (VOCs). Urban environments contain a variety of
VOCs from both anthropogenic and biogenic sources, as well as other species,
for instance nitrogen oxides (NO<span class="inline-formula"><sub><i>x</i></sub></span>), that can greatly influence the
formation pathways of condensable vapors like HOMs. During the last decade,
our understanding of HOM composition and formation has increased
dramatically, with most experiments performed in forests or in heavily
polluted urban areas. However, studies on the main sources for condensable
vapors and secondary organic aerosols (SOAs) in biogenically influenced urban
areas, such as suburbs or small cities, have been limited. Here, we studied
the HOM composition, measured with two nitrate-based chemical ionization
mass spectrometers and analyzed using positive matrix factorization (PMF),
during late spring at two locations in Helsinki, Finland. Comparing the
measured concentrations at a street canyon site and a nearby urban
background station, we found a strong influence of NO<span class="inline-formula"><sub><i>x</i></sub></span> on the HOM
formation at both stations, in agreement with previous studies conducted in
urban areas. Even though both stations are dominated by anthropogenic VOCs,
most of the identified condensable vapors originated from biogenic
precursors. This implies that in Helsinki anthropogenic activities mainly
influence HOM formation by the effect of NO<span class="inline-formula"><sub><i>x</i></sub></span> on the biogenic VOC
oxidation. At the urban background station, we found condensable vapors
formed from two biogenic VOC groups (monoterpenes and sesquiterpenes), while
at the street canyon, the only identified biogenic HOM precursor was
monoterpenes. At the street canyon, we also observed oxidation products of
aliphatic VOCs, which were not observed at the urban background station. The
only factors that clearly correlate (temporally and composition-wise)
between the two stations contained monoterpene-derived dimers. This suggests
that HOM composition and formation mechanisms are strongly dependent on
localized<span id="page12966"/> emissions and the oxidative environment in these biogenically
influenced urban areas, and they can also change considerably within
distances of 1 km within the urban environment. This further
suggests that studies should be careful when extrapolating single-point
measurements in an urban setting to be representative of district or city
scales.</p> |
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ISSN: | 1680-7316 1680-7324 |