P1253296800jnUyg - PowerPoint PPT Presentation

Title: P1253296800jnUyg


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Tropospheric Organic Chemistry Experiment
TORCH - Part of the Polluted Troposphere
programme -approx. 1.0 M funding over 3
years - Started 1st Nov 2002 - 7 Universities /
10 depts - Leeds, York, UEA, Leicester,
Imperial, Kings, UMIST
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• Aims
• Increase understanding of the role played by
  primary and
• partially oxidised organic species in gas phase
  photochemistry,
• Develop thermodynamic and microphysical
  descriptions of
• organic aerosol and use them to develop improved
  models of
• behaviour in the atmosphere
• Investigate the production, composition and
  evolution of organic
• aerosol and links with gas phase organic
  oxidation.

Model development and validation against two
large UK field experiments. First near field,
second downwind
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Background

• UK detailed gas phase chemistry experiments to
  date
• many in Clean air - e.g. ACSOE, NAMBLEX,
  SOAPEX
• some Urban air - e.g. PUMA
• Recent experiments have shown surprising results
• In clean air oxidised organic are a very
  significant OH sink
• evidence for long range transport of oxidised by
  products from US
• In polluted air OH remains high in winter despite
• OH sustained through O3 organic reactions and
  carbonyl photolysis

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C2-C7 NMHCs
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Time / mins
acetaldehyde
ethanol
methacrolien
acetone
Methanol
benzene
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MVK

• Sum NMHCAll NMHC except ethane.
• Sum O-VOCAcetone Acetaldehyde Methanol
  Methacrolein concentrations.
• Only in periods of anticyclonic local easterly
  pollution does the mass sum of the NMHC compare
  to the sum of the O-VOC.

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10
Time / mins
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Fractional organic contributions as OH sinks
Including only acetone, methanol and
acetaldehyde as O-VOCs
Using all O-VOCs from GCxGC plus dual channel GC
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Comparison of OH and J(O1D) diurnals in summer
and winter during PUMA
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• Limited detailed chemical data on polluted
  airmasses
• downwind of source (SOS in US, BERLIOZ in
  Germany)
• Generally the focus has been on comparison of
  measurements
• with model prediction of O3 and OH
• O3 measure of time integrated processes
• OH measure of instantaneous processes
• BUT this gives little information on the
  validity of the route or
• rates which link them, - need direct
  measurements of intermediates
• e.g. stable aldehydes, ketones and alcohols
• This validation is required to ensure correct
  predictions under
• future emission and climate scenarios

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• Aerosols previously dealt with separately to gas
  phase oxidation
• However increasing awareness of organic element
  in both primary
• and secondary aerosol and that this composition
  changes with
• airmass age and processing
• Minor mass route loss compared to gas phase
  oxidation but
• important in influencing aerosol properties
• Uptake of oxidised material is directly linked
  with rates and routes
• of gas phase oxidation
• Recent chamber studies (e.g. Toluene)
• Can we link mechanistic and kinetic predictions
  of organic
• oxidation with observations in gas phase, and
  partitioning with
• observations in aerosol phase ?

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M. Rami Alfarra, UMIST
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• Why are we now in a position to attempt this?
• Detailed models such as MCMv3 now in advanced
  state
• Can offer predictions of key target intermediates
• Moving from zero dimensions to trajectory
• Probing the evolution of the airmass
• Improved information of gas phase oxidation
  pathways
• data from chamber experiments
• Better treatment of organic aerosol
  thermodynamics
• Measurements
• Specifically big advances in measurement
  capability in some
• key areas relating to partially oxidised
  material
• More generally Huge community wide improvement
  in gas and

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• Examples
• As recent as 4-5 years ago, carbonyl measurements
  were possible
• only through long integration low sensitivity
  indirect derivitisation methods.
• Now
• on-line direct measurements of carbonyl compounds
  with
• a variety of approaches
• GC, PTR-MS and PTR-TOF
• Higher molecular weight organics with GCxGC
• Extensive radical instrumentation now available
• Direct aerosol composition with Aerosol MS
• Size specific composition by coupling aerosol
  mobility with MS

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Purpose of experimental phase
(I) To produce a large high quality data set on
the composition and properties of both gases and
aerosols within the polluted boundary layer
within 2-24 hours from point of emission. (ii)
To compare the observed speciation and abundance
of partially oxidised organics with that
predicted using current emissions inventories and
the MCMv3 (iii) compare measured radical and O3
concentrations with results from comprehensive
chemical mechanisms, (iv) determine oxygenate
and organic nitrate modification of
photochemistry downwind of a pollution
source, (v) establish a more complete inventory
of the source and sink species that control OH,
HO2 and RO2 concentrations in semi-polluted to
polluted air. (vi) To provide speciated
information on condensable organic material in
gas phase under near field and down wind
conditions
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Whos who in TORCH
Key 1. Lab validation, 2. Field expt, 3. Gas
phase chemistry, 4. Gas/particle partitioning,
5. SOA ageing, 6. SOA parameterisation, 7. SOA
precursors, 8. Regional modelling C Activity
Co-ordinator
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Experimental phase 1 Near-field experiment 21st
July - 5 Sept 2003 Writtle College nr Chelmsford
Flat topography Rural location 10 miles from
M25 20 miles central London No major emissions
from edge of M25 to site 1-2 hours airmass
transit time 100kva power
Using extensive UFAM facilities GC / FAGE /
Aerosol containers UEA trailer extra lab
accommodation computing suite
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Chemical Species Technique DL F Institute Gas
Phase Ozone UV Photometric 1
ppb 10s UEA/Leeds/Leicester Water
Vapour IR 1 1 s Leeds Temperature
T AWS 0.1 1 s UFAM Local wind AWS 1s UFAM
Peroxyacetylnitrate GC 0.1-5 ppt
1 hour Leeds aromatics, alcohols, ketones,
aldehydes, ethers GC-FIDx2 2D-GC 0.1-5 ppt 1
hour Leeds Carbon monoxide CO VUV fluorescence 1
ppb, 1 s UEA Organic nitrates NICI-GC-MS Sub
ppt 1 hour
UEA Semivolatile VOCs 2DGC 0.1-5 ppt
4 hours Leeds Oxygenates PTR-MS 10 ppt
10s UEA Oxygenates PTR-TOF 10ppt
10s York PAN, MPAN, PPN PTR-MS 70ppt
15s Nitric oxide NO Chemiluminescence 10
ppt, 1 m UEA Nitrogen dioxide NO2 Photolysis
chemiluminescence 10 ppt, 1 m UEA Nitric Acid
HNO3 Tuneable Diode Laser 100ppt
1s UMIST Ammonia NH3 Tuneable Diode
Laser 100ppt 1s UMIST NO2 photolysis
j(NO2) Photometer 1 s Leicester O3 photolysis
j(O1D) Fixed bandwidth radiometry, 1
s Leicester Photolysis rates Spectral
radiometry 1m Leicester Speciated
peroxides (inorganic and organic) Enzyme
Fluorimetry 20 ppt, 10 s UEA Formaldehyde Hants
ch Reaction 50 ppt, 10 s UEA SO2 Pulsed
Fluorescence 1ppb 1 m UEA Peroxy
radicals (RO2 HO2) Chemical amplifier PERCA 1
ppt, 1m UEA/Leicester OH HO2 FAGE
0.04 ppt/ 10s 0.1 ppt Leeds Aerosols Aeros
ol number and size distributions SMPS (3-500nm),
optical particle counters (0.1-300?m) 10
minutes UMIST CN Light Scattering (TSI) 7 nm
10 sec UEA/UMIST Total/Ultra fine
particles gt 3 nm TSI 3025 gt10 nm TSI 3010 1
sec UMIST Aerosol chemical composition Aerodyne
AMS 100 particles/s 0.25 ?g m-3
UMIST impactors (NH4, Na, Cl-, SO42-),
3-12 hrs UMIST/ISAO, Bologna Water Soluble
Organics, incl. Functionality as a function of
molecular weight (ISAO, Fuzzi) impactors for
EC/OC commercial lab analysis UMIST
Hygroscopic Growth factor DMA (H-TDMA) 1
hour UMIST
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Additional measurements Aberwsytwth Dopplar
wind profiler Ozone profiler (test
expt) Limited vertical chemical profiles using
Dornier 228 aircraft with CO / O3 met / canister
samples. Others?
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• Experimental phase 2
• Downwind experiment summer 2004
• Weybourne Atmospheric Observatory
• Long historical data series
• Contrasting airmasses
• 8-16 hour transit time from London. Also air
  from midlands
• Combined experiment with FAAM aircraft and
  CLOPAP.
• Vertical structure over site determined by
  aircraft operating offshore
• Inclusion of Bristol O-VOC GC instrument