PTR-MS / PTR-TOF-MSVOC fluxes during NOMAADS

NCAR, NOAA, NILU, UIBK

PTR-MS

)()(1][

3

OHcps

VOCHcpstk

VOC

Proton transfer reaction

Calculation of the neutral concentration

OHVOCHVOCOH k23

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 MirageMIRAGE/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 PTR-MS

PTR-TOF-MS footprint

POWER: 120V/1000WWeight: 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

• Horizontal gradients (land cover characterization)

• Vertical gradients (flux divergence measurements)

Will need 20 Hz data stream post-flight

2011 CIRPAS Twin OtterNCAR/UC Berkeley/CIRPAS

Horizontal PBL gradients

160.76 160.78 160.8 160.82 160.84 160.86 160.88 160.9 160.920

500

1000

1500

2000

2500

doy

Alti

tude

(m)

Radar Altimeter (m)Ground elevation (m)Altitude (m a.s.l)Altitude (m a.g.l.)

PBL soundings

Altitude above ground – PBL height

160.75 160.8 160.85 160.90

500

1000

1500

2000Extrapolated PBL

Forest: fetch about 10 x PBL height

20 nm

1 nm

View from top

PBL

Flight track

Race track

Sounding (up to 4000-7000 ft depending on PBL) at beginning and end of each profileSounding 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

Saw tooth sounding on outbound and inbound legs

Spiral

surface

Synoptic Wind

1 track is about 30 minutesEntire profile is about 1.5 hours at

70 m/s

Profiles flown during CABERNET

wind

Flux divergence

-0.3 -0.1 0.1 0.3 0.5 0.7 0.9 1.1 1.30

0.2

0.4

0.6

0.8

1

1.2

1.4

isoprenewTqw

normalized flux

z/zi

Determine OH:4 x 106 molecules / cm3

Surface flux

Entrainment flux

MEGAN - Model of Emissions of Gases and Aerosols from Nature

OA

K W

OO

DLA

ND

S

Flux processing (FFT and wavelet decomposition)

-6000 -4000 -2000 0 2000 4000 6000-1

-0.5

0

0.5

1

1.5

2

2.5

3

3.5 x 104

0 20 40 60 80 100-10

0

10

[c -

mea

n(c)

]/sqr

t(c) a) VOC

0 20 40 60 80 100

2 4 8

163264

b) Wavelet Cross Spectrum

Perio

d (s

)

0

0.5

1

0 20 40 60 80 100-10

0

10

Distance [km]

Av.

cro

ssva

rianc

e d) Scale-average Time Series

10-3 10-2 10-1 100 101-1

-0.5

0

0.5

1

1.5

Hz

f x

CoS

<w' 'T' 'fft>

<w' 'VOC' 'fft>

<w' 'T' 'wave>

<w' 'VOC' 'wave>

566.4342 56.64342 5.664342 0.5664342 0.05664342km

10-4 10-3 10-2 10-1 100 101-1

-0.5

0

0.5

1

1.5

Hz

f x C

oS

<w' 'T' 'fft>

<w' 'VOC' 'fft>

<w' 'T' 'wave>

<w' 'VOC' 'wave>

Flux divergenceEntrainment Flux

z/h

PBL top

Flux

Surface Flux

Reactive compound

More reactive compound

Flux profile = function of Dahmkoehler number Da

Da = mixing timescale / chemical timescale