Comprehensive analysis of particle growth rates from nucleation mode to cloud condensation nuclei in boreal forest
<p>Growth of aerosol particles to sizes at which they can act as cloud condensation nuclei (CCN) is a crucial factor in estimating the current and future impacts of aerosol–cloud–climate interactions. Growth rates (GRs) are typically determined for particles with diameters (<i>d</i...
| Main Authors: | , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-08-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/12085/2018/acp-18-12085-2018.pdf |
| Summary: | <p>Growth of aerosol particles to sizes at which they can act as cloud
condensation nuclei (CCN) is a crucial factor in estimating the current and
future impacts of aerosol–cloud–climate interactions. Growth rates (GRs) are
typically determined for particles with diameters (<i>d</i><sub>P</sub>) smaller than 40 nm immediately after a regional new particle formation (NPF) event. These
growth rates are often taken as representatives for the particle growth to
CCN sizes (<i>d</i><sub>P</sub> > 50–100 nm). In modelling frameworks, the
concentration of the condensable vapours causing the growth is typically
calculated with steady state assumptions, where the condensation sink (CS) is the
only loss term for the vapours. Additionally, the growth to CCN sizes is
represented with the condensation of extremely low-volatility vapours and
gas–particle partitioning of semi-volatile vapours. Here, we use a novel
automatic method to determine growth rates from below 10 nm to hundreds
of nanometres from a 20-year-long particle size distribution (PSD) data set in
boreal forest. With this method, we are able to detect growth rates also at
times other than immediately after a NPF event. We show that the GR increases
with an increasing oxidation rate of monoterpenes, which is closely coupled
with the ambient temperature. Based on our analysis, the oxidation reactions
of monoterpenes with ozone, hydroxyl radical and nitrate radical all are
capable of producing vapours that contribute to the particle growth in the
studied size ranges. We find that GR increases with particle diameter,
resulting in up to 3-fold increases in GRs for particles with <i>d</i><sub>P</sub>  ∼  100 nm in comparison to those with <i>d</i><sub>P</sub>  ∼  10 nm. We use a
single particle model to show that this increase in GR can be explained with
aerosol-phase reactions, in which semi-volatile vapours form non-volatile
dimers. Finally, our analysis reveals that the GR of particles with <i>d</i><sub>P</sub> < 100 nm is not limited by the condensation sink, even though the GR
of larger particles is. Our findings suggest that in the boreal continental
environment, the formation of CCN from NPF or sub-100 nm emissions is more
effective than previously thought and that the formation of CCN is not as
strongly self-limiting a process as the previous estimates have suggested.</p> |
|---|---|
| ISSN: | 1680-7316 1680-7324 |