Background aerosol over the Himalayas and Tibetan Plateau: observed characteristics of aerosol mass loading
To investigate the atmospheric aerosols of the Himalayas and Tibetan Plateau (HTP), an observation network was established within the region's various ecosystems, including at the Ngari, Qomolangma (QOMS), Nam Co, and Southeastern Tibetan (SET) stations. In this paper we illustrate aerosol mass...
| Main Authors: | , , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-01-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/17/449/2017/acp-17-449-2017.pdf |
| Summary: | To investigate the atmospheric aerosols of the Himalayas and Tibetan Plateau
(HTP), an observation network was established within the region's various
ecosystems, including at the Ngari, Qomolangma (QOMS), Nam Co, and
Southeastern Tibetan (SET) stations. In this paper we illustrate aerosol mass
loadings by integrating in situ measurements with satellite and ground-based
remote sensing datasets for the 2011–2013 period, on both local and large
scales. Mass concentrations of these surface atmospheric aerosols were
relatively low and varied with land cover, showing a general tendency of
Ngari and QOMS (barren sites) > Nam Co (grassland site) > SET
(forest site). Daily averages of online PM<sub>2.5</sub>
(particulates with aerodynamic diameters below 2.5 µm) at these
sites were sequentially 18.2 ± 8.9, 14.5 ± 7.4, 11.9 ± 4.9
and 11.7 ± 4.7 µg m<sup>−3</sup>. Correspondingly, the ratios of
PM<sub>2.5</sub> to total suspended particles (TSP) were 27.4 ± 6.65,
22.3 ± 10.9, 37.3 ± 11.1 and 54.4 ± 6.72 %. Bimodal
mass distributions of size-segregated particles were found at all sites, with
a relatively small peak in accumulation mode and a more notable peak in
coarse mode. Diurnal variations in fine-aerosol masses generally displayed a
bi-peak pattern at the QOMS, Nam Co and SET stations and a single-peak
pattern at the Ngari station, controlled by the effects of local
geomorphology, mountain-valley breeze circulation and aerosol emissions. Dust
aerosol content in PM<sub>2.1</sub> samples gave fractions of 26 % at the Ngari
station and 29 % at the QOMS station, or ∼ 2–3 times that of
reported results at human-influenced sites. Furthermore, observed evidence
confirmed the existence of the aerodynamic conditions necessary for the
uplift of fine particles from a barren land surface. Combining surface
aerosol data and atmospheric-column aerosol optical properties, the TSP mass
and aerosol optical depth (AOD) of the Multi-angle Imaging Spectroradiometer
(MISR) generally decreased as land cover changed from barren to forest, in
inverse relation to the PM<sub>2.5</sub> ratios. The seasonality of aerosol mass
parameters was land-cover dependent. Over forest and grassland areas, TSP
mass, PM<sub>2.5</sub> mass, MISR-AOD and fine-mode AOD were higher in spring and
summer, followed by relatively lower values in autumn and winter. At the
barren site (the QOMS station), there were inconsistent seasonal patterns
between surface TSP mass (PM<sub>2.5</sub> mass) and atmospheric column AOD
(fine-mode AOD). Our findings implicate that HTP aerosol masses (especially
their regional characteristics and fine-particle emissions) need to be
treated sensitively in relation to assessments of their climatic effect and
potential role as cloud condensation nuclei and ice nuclei. |
|---|---|
| ISSN: | 1680-7316 1680-7324 |