Molecular markers of biomass burning and primary biological aerosols in urban Beijing: size distribution and seasonal variation
<p>Biomass burning and primary biological aerosol particles account for an important part of urban aerosols. Floods of studies have been conducted on the chemical compositions of fine aerosols (PM<span class="inline-formula"><sub>2.5</sub></span>) in megacitie...
| Main Authors: | , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/20/3623/2020/acp-20-3623-2020.pdf |
| Summary: | <p>Biomass burning and primary biological aerosol particles
account for an important part of urban aerosols. Floods of studies have been
conducted on the chemical compositions of fine aerosols (PM<span class="inline-formula"><sub>2.5</sub></span>) in
megacities where the haze pollution is one of the severe environmental
issues in China. However, little is known about their size distributions in
atmospheric aerosols in the urban boundary layer. Here, size-segregated
aerosol samples were collected in Beijing during haze and clear days from
April 2017 to January 2018. Three anhydrosugars, six primary saccharides and
four sugar alcohols in these samples were identified and quantified by gas
chromatography/mass spectrometry (GC/MS). Higher concentrations of a biomass
burning tracer, levoglucosan, were detected in autumn and winter than in other
seasons. Sucrose, glucose, fructose, mannitol and arabitol were more
abundant in the bloom and glowing seasons. A particularly high level of
trehalose was found in spring, which was largely associated with the Asian
dust outflows. Anhydrosugars, xylose, maltose, inositol and erythritol
are mainly present in the fine mode (<span class="inline-formula"><2.1</span> <span class="inline-formula">µ</span>m), while the others
showed the coarse-mode preference. The concentrations of measured tracers of
biomass burning particles and primary biological particles in the haze
events were higher than those in the non-hazy days, with enrichment factors
of 2–10. Geometric mean diameters (GMDs) of molecular markers of biomass
burning and primary biological aerosols showed that there was no significant
difference in the coarse mode (<span class="inline-formula">>2.1</span> <span class="inline-formula">µ</span>m) between the haze
and non-haze samples, while a size shift towards large particles and large
GMDs in the fine fraction (<span class="inline-formula"><2.1</span> <span class="inline-formula">µ</span>m) was detected during the
hazy days, which highlights that the stable meteorological conditions with
high relative humidity in urban Beijing may favor the condensation of
organics onto coarse particles.The contributions of reconstructed primary
organic carbon (POC) by tracer-based methods from plant debris, fungal
spores and biomass burning to aerosol OC in the total-mode particles were
in the ranges of 0.09 %–0.30 % (on average 0.21 %), 0.13 %–1.0 %
(0.38 %) and 1.2 %–7.5 % (4.5 %), respectively. This study demonstrates
that the contribution of biomass burning was significant in Beijing
throughout the whole year with the predominance in the fine mode, while the
contributions of plant debris and fungal spores dominated in spring and
summer in the coarse mode, especially in sizes <span class="inline-formula">>5.8</span> <span class="inline-formula">µ</span>m. Our observations demonstrate that the sources, abundance and chemical
composition of urban aerosol particles are strongly size dependent in
Beijing, which is important to better understand the environmental and
health effects of urban aerosols and should be considered in air quality and climate models.</p> |
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| ISSN: | 1680-7316 1680-7324 |