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| Titel |
FIGAERO ToF CIMS measurements of chlorine photochemical activation by nitryl chloride chemistry at a semi-rural site in Beijing |
| VerfasserIn |
Michael Le Breton, Åsa M. Hallquist, Ravi Kant Pathak, David Simpson, Yujue Wang, Jing Zheng, Yudong Yang, Dongjie Shang, Haichao Wang, Keding Lu, Song Guo, Min Hu, Mattias Hallquist |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250140901
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| Publikation (Nr.) |
 EGU/EGU2017-4353.pdf |
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| Zusammenfassung |
| Severe pollution events across China pose a major threat to air quality and climate through
the direct emission of pollutants, but also via the production of photochemically induced
secondary pollutants. Nitryl chloride (ClNO2), produced from heterogeneous reactions of
dinitrogen pentoxide (N2O5) and aerosols containing chloride, is photolysed rapidly in
sunlight and activates chlorine. Subsequent daytime oxidation via the chlorine atom can
proceed orders of magnitude faster than that of the hydroxyl radical and therefore
significantly perturb radical budgets and concentrations of ozone and secondary pollutants.
Knowledge of the formation pathways, abundance and fate of these secondary pollutants,
which can depend on ClNO2 abundance, is not fully understood but is necessary to support
abatement strategies which will efficiently account for both primary and secondary
pollutants.
A Time of Flight Chemical Ionisation Mass Spectrometer (ToF CIMS) utilising the Filter
Inlet for Gases and AEROsols (FIGAERO) was deployed in Changping, Beijing, during June
and July, 2016 as part of an intercollaborative project to assess the photochemical smog in
China. Concentrations of ClNO2 regularly exceeded 500 ppt throughout the campaign
and reached a maximum concentration of 2.8 ppb, whereas relatively low N2O5
concentrations were observed, indicating a rapid heterogeneous production of ClNO2.
Correlation of particulate chloride and carbon monoxide during the campaign suggests an
anthropogenic chlorine source, also supported by high daytime Cl2 concentrations.
Observations of ClNO2 desorptions using the FIGAERO suggest a possible unaccounted
particulate reservoir of active chlorine in highly polluted regions. The persistence of
ClNO2 several hours passed sunrise significantly increases the atomic chlorine
production rate throughout the day further perturbing standard daytime oxidation
processes.
Simultaneous ToF CIMS measurements of Cl2, ClNO2, HCl, HOCl, OClO and
ClONO2 were implemented into steady state calculations using the Master Chemical
Mechanism (MCM) to assess how the daytime activation of chlorine competes
with OH as a dominant oxidant in this heavily polluted region. The reactions of
atomic chlorine with VOCs are traced and assessed via the gas and particle phase
measurements of chlorinated VOCs and supporting Proton Transfer Reaction Mass
Spectrometer (PTR MS) VOC measurements. This provides the first high frequency
measurements of unique tracers for chlorine atom chemistry, several of which are
represented in the MCM, in both the gas and particle phase and enable the detailed
assessment of their diurnal variation and importance for photochemical smog formation. |
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