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

NCAR, NOAA, NILU, UIBK

PTR-MS

)(

)(1][

3

OHcps

VOCHcps

tkVOC

Proton transfer reaction

Calculation of the neutral concentration

OHVOCHVOCOH k

23

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 PTR-MS

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

• Horizontal gradients (land cover characterization)

• Vertical gradients (flux divergence measurements)

Will need 20 Hz data stream post-flight

2011 CIRPAS Twin Otter NCAR/UC Berkeley/CIRPAS

Horizontal PBL gradients

160.76 160.78 160.8 160.82 160.84 160.86 160.88 160.9 160.92

0

500

1000

1500

2000

2500

doy

Alt

itu

de (

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

2000

Extrapolated 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 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

Saw tooth sounding on outbound and inbound legs

Spiral

surface

Synoptic Wind

1 track is about 30 minutes Entire profile is about 1.5 hours at

70 m/s

Profiles flown during CABERNET

Flux divergence

0

0.2

0.4

0.6

0.8

1

1.2

1.4

-0.3 -0.1 0.1 0.3 0.5 0.7 0.9 1.1 1.3

z/zi

normalized flux

isoprene

wT

qw

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

3.5x 10

4

0 20 40 60 80 100-10

0

10

[c -

mean

(c)]

/sq

rt(c

) a) VOC

0 20 40 60 80 100

2

4

8

16

32

64

b) Wavelet Cross Spectrum

Pe

rio

d (

s)

0

0.5

1

0 20 40 60 80 100-10

0

10

Distance [km]

Av

. c

ros

sv

ari

an

ce 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 C

oS

<w' 'T' 'fft

>

<w' 'VOC' 'fft

>

<w' 'T' 'wave

>

<w' 'VOC' 'wave

>

566.4342 56.64342 5.664342 0.5664342 0.05664342

km

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 divergence

Entrainment 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