Fragmentation patterns of particulate organic nitrates in an Aerosol Mass Spectrometer

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http://urn.fi/URN:NBN:fi:hulib-201912044058
Title: Fragmentation patterns of particulate organic nitrates in an Aerosol Mass Spectrometer
Author: Graeffe, Frans
Contributor: University of Helsinki, Faculty of Science
Publisher: Helsingin yliopisto
Date: 2019
Language: eng
URI: http://urn.fi/URN:NBN:fi:hulib-201912044058
http://hdl.handle.net/10138/308234
Thesis level: master's thesis
Degree program: Ilmakehätieteiden maisteriohjelma
Master's Programme in Atmospheric Sciences
Magisterprogrammet i atmosfärsvetenskaper
Specialisation: Aerosolifysiikka
Aerosol Physics
Aerosolfysik
Discipline: none
Abstract: Atmospheric aerosols affect the Earth's radiative balance, visibility and human health. Therefore the formation processes and growth of these particles are important and should be studied to understand how human and natural processes affects these processes. One poorly understood and relatively little studied part of aerosols is particulate organic nitrates (pONs). These pONs are mostly formed during nighttime when NOx, mainly emitted from fossil fuel combustion and industrial processes, and volatile organic compounds (VOCs), from both natural and anthropogenic sources, reacts in the atmosphere. The quantification of these pONs is still hard due to instrumental restrictions, although much improvement has happened during recent years. One main reason for these challenges is the difficulty to separate inorganic nitrates from organic nitrates with real-time instruments. During this work, we generated pure pON in well controlled laboratory conditions and sampled it with an Aerosol Mass Spectrometer (AMS), an instrument widely used for measuring the chemical composition of atmospheric aerosols. We used four different pON precursors to generate pON. I investigated the fragmentation patterns of pON detected by the AMS, utilizing the high resolution of the newest model of the AMS. As older versions of the AMS has difficulties to separate nitrate-containing organic fragments due to lower resolution than the AMS I used, I was able to study pON mass spectrum with better resolution than anyone before me. I found mass spectral differences for the different pON precursors, and was able to find unique fragments for some of the pON precursors that possibly can be used as marker fragments.


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