Chemical composition of nanoparticles from <i>α</i>-pinene nucleation and the influence of isoprene and relative humidity at low temperature
<p>Biogenic organic precursors play an important role in atmospheric new particle formation (NPF). One of the major precursor species is <span class="inline-formula"><i>α</i></span>-pinene, which upon oxidation can form a suite of products covering a wide rang...
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
Copernicus Publications
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/49e181487bc54896a3f154f556547c1d |
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| Sumario: | <p>Biogenic organic precursors play an important role in
atmospheric new particle formation (NPF). One of the major precursor species
is <span class="inline-formula"><i>α</i></span>-pinene, which upon oxidation can form a suite of products
covering a wide range of volatilities. Highly oxygenated organic molecules
(HOMs) comprise a fraction of the oxidation products formed. While it is
known that HOMs contribute to secondary organic aerosol (SOA) formation,
including NPF, they have not been well studied in newly formed particles due
to their very low mass concentrations. Here we present gas- and particle-phase chemical composition data from experimental studies of <span class="inline-formula"><i>α</i></span>-pinene oxidation, including in the presence of isoprene, at temperatures
(<span class="inline-formula">−</span>50 and <span class="inline-formula">−</span>30 <span class="inline-formula"><sup>∘</sup></span>C) and relative
humidities (20 % and 60 %) relevant in the upper free troposphere. The
measurements took place at the CERN Cosmics Leaving Outdoor Droplets (CLOUD)
chamber. The particle chemical composition was analyzed by a thermal
desorption differential mobility analyzer (TD-DMA) coupled to a nitrate
chemical ionization–atmospheric pressure interface–time-of-flight
(CI-APi-TOF) mass spectrometer. CI-APi-TOF was used for particle- and gas-phase measurements, applying the same ionization and detection scheme. Our
measurements revealed the presence of C<span class="inline-formula"><sub>8−10</sub></span> monomers and C<span class="inline-formula"><sub>18−20</sub></span>
dimers as the major compounds in the particles (diameter up to
<span class="inline-formula">∼</span> 100 nm). Particularly, for the system with isoprene added,
C<span class="inline-formula"><sub>5</sub></span> (C<span class="inline-formula"><sub>5</sub></span>H<span class="inline-formula"><sub>10</sub></span>O<span class="inline-formula"><sub>5−7</sub></span>) and C<span class="inline-formula"><sub>15</sub></span> compounds
(C<span class="inline-formula"><sub>15</sub></span>H<span class="inline-formula"><sub>24</sub></span>O<span class="inline-formula"><sub>5−10</sub></span>) were detected. This observation is consistent
with the previously observed formation of such compounds in the gas phase. However, although the C<span class="inline-formula"><sub>5</sub></span> and C<span class="inline-formula"><sub>15</sub></span> compounds do not easily nucleate,
our measurements indicate that they can still contribute to the particle
growth at free tropospheric conditions. For the experiments reported here,
most likely isoprene oxidation products enhance the growth of particles
larger than 15 nm. Additionally, we report on the nucleation rates measured
at 1.7 nm (<span class="inline-formula"><i>J</i><sub>1.7 nm</sub></span>) and compared with previous studies, we found lower
<span class="inline-formula"><i>J</i><sub>1.7 nm</sub></span> values, very likely due to the higher <span class="inline-formula"><i>α</i></span>-pinene and
ozone mixing ratios used in the present study.</p> |
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