Increased new particle yields with largely decreased probability of survival to CCN size at the summit of Mt. Tai under reduced SO<sub>2</sub> emissions
<p>Because anthropogenic sulfur dioxide (SO<span class="inline-formula"><sub>2</sub></span>) emissions have decreased considerably in the last decade, PM<span class="inline-formula"><sub>2.5</sub></span> pollution in China has...
| Main Authors: | , , , , , , , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-01-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/21/1305/2021/acp-21-1305-2021.pdf |
| Summary: | <p>Because anthropogenic sulfur dioxide (SO<span class="inline-formula"><sub>2</sub></span>) emissions have
decreased considerably in the last decade, PM<span class="inline-formula"><sub>2.5</sub></span> pollution in China has
been alleviated to some extent. However, the effects of reduced SO<span class="inline-formula"><sub>2</sub></span> on
the particle number concentrations and subsequent contributions of grown new
particles to cloud condensation nuclei (CCN) populations, particularly at
high altitudes with low aerosol number loadings, are poorly understood. In
contrast, the increase in provincial forest areas in China with rapid
afforestation over the last few decades expectedly increases the
biogenic emissions of volatile organic compounds and their oxidized products
as nucleating precursors therein. In this study, we evaluated the
campaign-based measurements made at the summit of Mt. Tai (1534 m a.s.l.)
from 2007 to 2018. With the decrease in SO<span class="inline-formula"><sub>2</sub></span> mixing ratios from 15 <span class="inline-formula">±</span> 13 ppb in 2007 to 1.6 <span class="inline-formula">±</span> 1.6 ppb in 2018, the apparent
formation rate (FR) of new particles and the net maximum increase in the
nucleation-mode particle number concentration (NMINP) in the spring campaign
of 2018 was 2- to 3-fold higher than those in the spring campaign of 2007 with
almost the same occurrence frequency of new particle formation (NPF) events.
In contrast, the campaign-based comparison showed that the occurrence
frequency, in which the maximum geometric median diameter of the grown new
particles (<span class="inline-formula"><i>D</i><sub>pgmax</sub></span>) was <span class="inline-formula">></span> 50 nm, decreased considerably from
43 %–78 % of the NPF events before 2015 to <span class="inline-formula"><</span> 12 % in
2017–2018. Assuming <span class="inline-formula">></span> 50 nm as a CCN threshold size at high
supersaturations, the observed net CCN production decreased from
3.7 <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>3</sup></span> cm<span class="inline-formula"><sup>−3</sup></span> (on average) in the five campaigns before
2015 to 1.0 <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>3</sup></span> cm<span class="inline-formula"><sup>−3</sup></span> (on average) in the two campaigns
in 2017–2018. We argue that the increases in the apparent FR and NMINP are
mainly determined by the availability of organic precursors that participate
in nucleation and initial growth, whereas the decrease in the growth
probability is caused by the reduced emissions of anthropogenic precursors.
However, large uncertainties still exist because of a lack of data on the
chemical composition of these smaller particles.</p> |
|---|---|
| ISSN: | 1680-7316 1680-7324 |