PTR-MS / PTR-TOF-MS
VOC fluxes during NOMAADS
NCAR, NOAA, NILU, UIBK
PTR-MS
Proton transfer reaction
k
H 3O   VOC 

VOCH   H 2O
Calculation of the neutral concentration
1 cps(VOCH  )
[VOC ] 

k  t cps( H 3O  )
Target compounds: Isoprene, isoprene oxidation products
PTR-MS
• Slides into 1 bay of C-130 rack
• 2nd bay needed for additional
options: i.e. inlet pump, calgas
• HIMIL inlet on C-130
requested
• For EC flux measurements we
can only monitor 2-3
compounds (ie. isoprene,
MVK+MAC and perhaps Meoh
or MT)
Rack during Mirage
MIRAGE/INTEX-B
Note: For NOMAADS we will need to
request space adjacent to PTRMS for inlet
pump and calibration unit
Alternative or complimentary
• Due to a broader chemistry focus of NOMAADS, a
PTR-TOF-MS is proposed to be flown in
collaboration between NILU, NOAA, UIBK and
NCAR instead or along with PTR-MS
• Instrument comes already prepackaged in a NASA
P-3 rack
• Inlet requirements will be the same as for PTRMS
PTR-TOF-MS
footprint
POWER: 120V/1000W
Weight: 600 lbs
PTR-MS (NCAR) vs PTR-TOF-MS (NILU/NOAA/UIBK/NCAR)
• PTR-TOF-MS advantages: no pre-selection of compounds needed –
we can measure the entire mass spectrum at 10 Hz
• LOD: similar btw. PTR-TOF-MS and PTR-MS for a nominal mass (i.e.
compound), but much lower for PTR-TOF-MS, when considering
that the instrument scans over the entire mass range
• PTR-TOF-MS disadvantage: somewhat lower sensitivity, but
probably acceptable for isoprene flux measurements
• PTR-TOF-MS will also have the option of a SRI (selective reagion
ionization) capability
EC flux leg flight patterns
Will need 20 Hz data stream post-flight
• Horizontal gradients (land cover characterization)
• Vertical gradients (flux divergence measurements)
2011 CIRPAS Twin Otter
NCAR/UC Berkeley/CIRPAS
Horizontal PBL gradients
2500
Radar Altimeter (m)
Ground elevation (m)
Altitude (m a.s.l)
Altitude (m a.g.l.)
PBL soundings
Altitude (m)
2000
1500
1000
500
0
160.76
160.78
160.8
160.82
160.84
doy
160.86
160.88
160.9
160.92
Altitude above ground – PBL height
2000
Extrapolated PBL
1500
1000
500
0
160.75
160.8
160.85
160.9
Synoptic Wind
Spiral
PBL
Saw tooth sounding on outbound and inbound legs
Flight track
Forest: fetch about 10 x PBL height
surface
Race track
20 nm
View from top
1 nm
1 track is about 30 minutes
Entire profile is about 1.5 hours at
70 m/s
Sounding (up to 4000-7000 ft depending on PBL) at
beginning and end of each profile
Sounding can be a “sawtooth” on the outbound
leg, should be a spiral between consecutive profiles
and a “saw tooth” on the inboundleg: climb rate
500 ft/min
Profiles flown during CABERNET
Flux divergence
Determine OH:
4 x 106 molecules / cm3
1.4
Entrainment flux
1.2
z/zi
1
0.8
isoprene
0.6
wT
0.4
qw
0.2
Surface flux
0
-0.3
-0.1
0.1
0.3
0.5
0.7
normalized flux
0.9
1.1
1.3
MEGAN - Model of Emissions of Gases and Aerosols from Nature
OAK WOODLANDS
[c - mean(c)]/sqrt(c)
Flux processing (FFT and wavelet decomposition)
4
3.5
x 10
3
2.5
Period (s)
2
1.5
1
0.5
a) VOC
10
0
-10
0
Av. crossvariance
-0.5
-1
-6000
-2000
56.64342
0
2000
4000
6000
km
5.664342 0.5664342 0.05664342
1
0.5
0
20
40
60
80
100
d) Scale-average Time Series
10
0
-10
0
20
40
60
Distance [km]
80
100
1.5
1
1
0.5
0.5
 f x CoS
f x CoS
1.5
566.4342
-4000
100
2
4
8
16
32
64
0
0
20
40
60
80
b) Wavelet Cross Spectrum
0
<w' 'T' ' >
0
fft
<w' 'T' ' >
fft
<w' 'VOC' ' >
fft
<w' 'VOC' ' >
fft
-0.5
<w' 'T' '
wave
<w' 'VOC' '
>
wave
-1
-4
10
-3
10
-2
-1
10
10
Hz
0
10
1
10
<w' 'T' 'wave >
-0.5
<w' 'VOC' '
>
wave
-1
-3
10
-2
10
-1
10
Hz
0
10
1
10
>
Flux divergence
Entrainment Flux
PBL top
Flux profile = function of Dahmkoehler number Da
Da = mixing timescale / chemical timescale
Reactive compound
z/h
More reactive compound
Surface Flux
Flux