Silicon-containing secondary organic aerosols in ambient air (Si-SOA)

Lead Research Organisation: University of Birmingham
Department Name: Sch of Geography, Earth & Env Sciences


This Pump-Priming project will initiate a new collaboration with a leading Chinese research group led by Prof Pingqing Fu at Institute of Atmospheric Physics (IAP-CAS). Our aim is to provide definitive evidence, for the first time, on the formation of silicon-containing secondary organic aerosols (Si-SOAs) via photochemical atmospheric processing by using the novel techniques at the IAP-CAS and the UoB. The wider project context is the oxidation of Si-containing volatile organic compounds (Si-VOCs), which are widely used in personal care products and industrial applications. Si-VOCs are the most abundant VOCs in indoor air and its concentration in Chinese megacities can be over 10 microgram per cubic meter (which is extremely high). Si-VOCs can be oxidised by hydroxyl radicals and form secondary organic aerosols (SOAs), which contributes to the regional haze pollution.

Our current NERC project Sources and Emissions of Air Pollutants in a Chinese Megacity - AIRPOLL-Beijing (NE/N007190/1) (2016 - 2020) integrates recent modelling, flux measurements, satellite retrievals, tower vertical profile measurements, and chemical transport modelling to provide thorough understanding of the sources and emissions of air pollutants in Beijing, at unprecedented detail and accuracy. As part of this project awarded to the University of Birmingham, we analyzed the chemical composition of individual particles collected during the winter campaign (Nov-Dec 2016) and found that >50% the fine particles contain silicon with mass fraction > 0.01. This suggests that silicon may play an important role in the formation of fine particles, which cause widespread smog / haze and lead to adverse human health effects. We also discovered that silicon is present as a coating, rather than as a solid grain, in individual sulphur-rich particles collected downwind of Chinese megacities, suggesting that the silicon is not directly emitted from primary sources (i.e., formed in the atmosphere). These new findings promoted us to hypothesize that silicon in the secondary particles in ambient air is formed from chemical processing of gas phase Si-containing VOCs.

Si-SOA project will rigorously test this hypothesis. To do this, we will apply a series of novel techniques to study silicon in fine particles for the first time. We will use STEM (Scanning Transmission Electron Microscopy) and NanoSIMS (Nanoscale Secondary Ion Mass Spectrometer) to speciate silicon in atmospheric fine particles and confirm whether silicon in individual secondary particles is present as organosilicon. If confirmed, thiswill provide "smoking gun" on the formation of silicon organic aerosol by atmospheric processing. We will also apply the ESI-HRMS (Electrospray ionisation - high resolution mass spectrometer) to identify Si-containing organic molecules in fine particles and then gas chromatography - mass spectrometer to quantify the concentration of Si-SOAs identified by ESI-HRMS in selected fine particle samples collected during the APHH-China campaigns.

Si-SOA project will add value to the AIRPOLL-Beijing by confirming the presence and quantify the concentration of siloxane oxidation products in fine particles. It will provide a better understanding on the sources of secondary organic aerosols, a key objective of AIRPOLL-Beijing. The project will consist of PI / research staff exchanges to plan and carry out the experiments in detail, followed by discussions on publication(s).

This proposal has been developed following discussions between SHI and FU at meetings in Beijing in May 2017, which was initiated by discovery of silicon as coating in individual secondary sulphate-rich particles and the detection of silicon in over 50% of individual fine particles (see above). In addition to the specific science goals, Si-SOA will nurture a developing collaboration between UK groups and leading Chinese researchers at IAP, with potential for future links.

Planned Impact

Si-SOA aims to advance our fundamental understanding of a potentially important aspect of air pollution - formation of silicon organic aerosols via atmospheric oxidation of silicon containing volatile organic compounds from the personal care products and industries. Accordingly, while the project will indirectly benefit many wider groups, the principal immediate beneficiaries are research scientists working in the field of atmospheric chemical processing and human health, and related areas, as noted above.

The wider scientific community will benefit from this work through the confirmation the oxidation process of silicon containing volatile organic compounds to form secondary organic aerosols and improvements in our understanding of secondary aerosol formation - ultimately leading to increased accuracy of model analyses of tropospheric composition.

-Policy makers: The finding in this project will raise awareness on the potential adverse health effects of silicon-containing volatile organic compounds from personal care products and industries, which may eventually lead to policy actions to control their emissions (following more in-depth research in the future). Through incorporation of the project results into atmospheric models (subsequently by other groups and/or in future research by ourselves) the accuracy of future atmospheric composition and climate predictions will be increased - of relevancy to policy formulation related to air quality modelling forecast. The identification of the oxidation products of silicon-containing organic compounds will also offer potential clues to their toxicity and bioaccumulation potential, which may promote regulatory control of such pollutants in the atmosphere.

- Personal care industry and general Public: Health effects of silicon-containing volatile organic compounds from personal care products and their oxidation products will be of interest to the general public and manufacturers. Research in this project will confirm whether these compounds will be oxidised in the atmosphere and quantify their contribution to regional haze pollution in China, which will be of relevance to other cities, in particular those density populated megacities such as Delhi and London. This will raise awareness of this under-recognized pollution.
Description Volatile methyl siloxanes (VMS) are widely used in personal care products and industrial applications, which can lead to aerosol formation in the atmosphere through oxidation by hydroxyl radical. Summer and winter PM2.5 samples were collected in Beijing. Inductively Coupled Plasma- Optical Emission Spectrometer (ICP-OES) was used to determine the total water soluble Si and spectrophotometer (UV-Vis) to investigate the total water soluble inorganic Si in PM2.5. Secondary organic Si was calculated by subtracting the water soluble inorganic Si from the total water soluble Si. We found that secondary organic Si accounts for approximately 73.5±24.6 % and 80.2±8.7 % of the total water soluble Si, and 0.63±0.55 % and 0.33±0.28 % of total Si in PM2.5 samples of urban Beijing during summer and winter, respectively.
Exploitation Route The newly established method for the estimation of secondary organic Si could be further applied by other users to quantify secondary organic Si in ambient aerosols. Moreover, the new developed LC-MSMS method for the determination of specific Si-containing organic compound (D4-OH) can be applied for future studies as well; more potential VMS oxidation products can be determined in the same manner.
Sectors Environment

Description Coupling of organic and inorganic aerosol systems in coastal atmosphere: the effect impact on secondary organic aerosol formation
Amount £110,000 (GBP)
Organisation The Royal Society 
Sector Charity/Non Profit
Country United Kingdom
Start 03/2019 
End 03/2022
Title PM2.5 analysis results of samples taken from the Institute of Atmospheric Physics -Beijing site by the Si-SOA project 
Description This dataset collection contains the results of the analysis conducted on PM2.5 (particulate matter) samples by the Si-SOA project. The PM2.5 samples were collected in the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences, China during August 2018 and January 2019 by the Silicon-containing secondary organic aerosols in ambient air (Si-SOA) project. The PM2.5 samples were taken from ambient air at the height of 8m and subjected to a series of analytical techniques, and the data collection is comprised of the following results. - The concentration of water-soluble Silicon/water-soluble organic Silicon/water-soluble inorganic Silicon in PM2.5 samples from Ultraviolet-Visible Spectrophotometry - The concentration of specific ions in PM2.5 samples from Ion Chromatography - The concentration of water-soluble Silicon in PM2.5 samples from Coupled Plasma - Optical Emission Spectrometry (ICP-OES) - The concentration of water-soluble elements in PM2.5 samples from Inductively Coupled Plasma Mass Spectrometry (ICP-MS) - The concentration of elements in PM2.5 samples from X-ray Fluorescence Spectrometry These data support the study of atmospheric processes in relation to fine Silicon-containing particles, which may contribute to the formation of haze and atmospheric pollution. 
Type Of Material Database/Collection of data 
Year Produced 2020 
Provided To Others? No  
Impact None identified 
Description Tianjin University 
Organisation Tianjin University
Country China 
Sector Academic/University 
PI Contribution We designed the experiments.
Collaborator Contribution Professor Pingqing Fu's group supported the field sampling in both summer and winter.
Impact The project is ongoing with no direct output yet.
Start Year 2018
Description Zhejiang University: Weijun Li 
Organisation Zhejiang University
Country China 
Sector Academic/University 
PI Contribution Data analysis, unique samples, fieldwork support, student training, and paper writing
Collaborator Contribution Manpower in field and laboratory measurements, instruments for signle particle collection, data for joint publications
Impact Research focused on understanding the sources, aging and processes of airborne particles using single particle analysis techniques including TEM and NanoSIMS. Recent research aims to better understand what controls the solubility of iron in the fine particles in urban atmosphere.
Start Year 2018