Explore. Discover. Understand. AIR-BROADENED LINE WIDTHS AND SHIFTS IN THE ν 3 BAND OF 16 O 3 AT...

Explore. Discover. Understand.

AIR-BROADENED LINE WIDTHS AND SHIFTS IN THE ν3 BAND OF 16O3 AT

TEMPERATURES BETWEEN 160 AND 300 K

M. A. H. SMITH and C. P. RINSLANDNASA Langley Research Center, Hampton, VA 23681-2199 U.S.A.

V. MALATHY DEVI and D. CHRIS BENNERThe College of William and Mary, Williamsburg, VA 23187-8795 U.S.A.

A. M. COXNew Horizons Governor’s School for Science and Technology, Hampton, VA 23666 and Poquoson High School, Poquoson, VA 23662 U.S.A.


Good vs. Bad Ozone

“Good” Ozone in the Stratosphere (10 – 40 km) Produced from photodissociation of O2 molecules Peak O3 concentrations at ~ 25 km Protects life from harmful shortwave UV radiation Destroyed by compounds such as CFCs released into the

atmosphere Significant depletion contributes to cooling of the stratosphere

“Bad” Ozone in the Troposphere (0 – 10 km) Produced in photochemical smog Toxic to animals (including humans) when inhaled Causes damage to plants A greenhouse gas in the upper troposphere Reacts to cleanse the troposphere of some pollutants


Tropospheric Ozone Measured from Space

• Since 1978 the Total Ozone Mapping Spectrometer (TOMS) instruments have been measuring global ozone levels from a variety of satellites. Instruments aboard the Aura satellite launched in 2004 are continuing the long term monitoring of ozone.

• Learn more about tropospheric ozone at http://earthobservatory.nasa.gov/


Global Average Temperature Profile

Tropopause temperatures vary with latitude and season, and are typically below 195 K in the tropics.


Hurricanes and Ozone

Ozone column measurements collected over Hurricane Erin on September 12, 2001 by the TOMS instrument on NASA’s Earth Probe satellite

In the eye, where air from the stratosphere is transported downward, ozone concentrations are elevated (yellow and green).

The core is surrounded by an area of much lower ozone concentrations (purple and blue) due to ozone-poor surface air being transported upward by strong thunderstorms.

Dropping ozone levels around the eye may be sign that a storm is strengthening.

From http://earthobservatory.nasa.gov/


Spectra Used for Ozone Fits in the ν3 Band

NO. OF DATE SAMPLE VMR TEMPERATURE PRESSURE PATH BAND RES.

SPECTRA (%) (K) (TORR) (m) PASS (cm-1)

2 10-Nov-94 O3 + Air 4.7 300 101, 204 0.0998 2 0.00272 10-Nov-94 O3 + Air 3.6 300 76, 153 0.0998 2 0.00274 7-Feb-96 O3 81 - 90 300 0.3 - 0.5 0.0998 2 0.00271 29-Apr-97 O3 30.3 298 1.3 0.500 2 0.00522 30-Apr-97 O3 + Air 0.6 297 110, 201 0.500 2 0.00523 1-May-97 O3 + Air 0.5 272 101 - 220 0.500 1 0.00523 2-May-97 O3 + Air 0.4 254 107 - 216 0.500 1 0.00523 4-May-97 O3 + Air 0.3 233 104 - 220 0.500 1 0.00525 6-May-97 O3 + Air 0.3 213 86 - 201 0.500 1 0.00521 21-May-98 O3 13 170 2.2 0.095 1 0.0053 21-May-98 O3 + Air 1.5 186 94 - 193 0.095 1 0.0051 22-May-98 O3 + Air 1.9 160 203 0.095 2 0.0051 22-May-98 O3 + Air 1.9 168 134 0.095 2 0.005

Band pass 1 = 500-1400 cm-1; Band pass 2 = 800-1400 cm-1

All spectra were recorded using the McMath-Pierce FTS with KCl beam splitter, 8 mm aperture, and He-cooled As:Si detectors.

February 1996 spectra were used in the intensity study published in JGR (Smith et al., 2001).

May 1998 spectra were recorded using a single detector.


Example of a Measured Spectrum

Ozone Spectrum 818

Wavenumber

1021 1022 1023 1024 1025

Tra

nsm

itta

nce

0.0

0.2

0.4

0.6

0.8

1.050-cm cell

0.3 % O3 in air

p = 86.2 torr

T = 213 K

Resolution = 0.0052 cm-1

▲ Red triangles mark lines for which parameters were determined.


Multispectrum Fitting Strategy

1) Four low-pressure spectra for which concentrations were determined by UV absorption (254 nm) were fit together first to obtain absolute line intensities.

2) Intensities were fixed to these retrieved values for subsequent fitting of air-broadened spectra.

3) Room-temperature air-broadened spectra were added to the fit first, followed by the lower-temperature spectra down to 213 K.

4) Noisy spectra from 186 to 160K were added to the fit with low weights due to relatively poor Signal-to-Noise.

5) Parameters have been determined for 41 P-branch lines in the spectral region 1016 – 1025 cm-1 (J˝ = 15 – 26, Ka˝ = 0 – 11).


Results: Intensities

J"

14 16 18 20 22 24 26 28

Inte

nsi

ty R

atio

0.94

0.96

0.98

1.00

1.02

1.04

1.06

1.08

1.10

Present Work / HITRAN 2004, Mean = 1.041, SD = 0.013Present Work / HITRAN 2000, Mean = 1.008, SD = 0.013Present Work / Smith et al. (2001), Mean = 1.003, SD = 0.003


Results: Broadening Coefficients

J"

14 16 18 20 22 24 26 28

bL

0 (

cm-1

atm

-1)

at 2

96K

0.064

0.068

0.072

0.076

0.080

0.084

0.088

HITRAN 2004 (air)HITRAN 2000 (air)Spencer et al., 1992 (N2)

Present Work (air)


Results: Broadening Temperature Dependence Exponents

J"

14 16 18 20 22 24 26 28

n

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

HITRAN 2004 (air)HITRAN 2000 (air)Spencer et al., 1992 (N2)

Present Work (air)

b = b0(T0/T)n


Results: Pressure-Induced Line Shifts

J"

14 16 18 20 22 24 26 28

0 (c

m-1

atm

-1) a

t 296

K

-0.012

-0.010

-0.008

-0.006

-0.004

-0.002

0.000

0.002

0.004

(Present Work)

(Malathy Devi et al., 1997)

1 (Smith et al., 1997)

HITRAN 2004


Results: Temperature Dependences of Pressure-Induced Line Shifts

J"

14 16 18 20 22 24 26 28

' (

cm-1

atm

-1 K

-1)

-8e-5

-6e-5

-4e-5

-2e-5

0

2e-5

4e-5

6e-5

8e-5

1e-4

3

2

1

0(T) = 0(T0) + ' (T-T0)


Comparison with the Other Fundamental Bands

Broadening Coefficients

J"

14 16 18 20 22 24 26 28

bL

0 (c

m-1

atm

-1) a

t 296

K

0.070

0.075

0.080

0.085

0.090

3

Calc 3

Calc 1

Temperature Dependence Exponents

J"

14 16 18 20 22 24 26 28n

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Measured values are from Present Work, Malathy Devi et al. (1997) and Smith et al. (1997).

Calculated values are based on empirical formulas given by Wagner et al. (2002).


Comparison with Overtone Band

Air-Broadening Coefficients

J"

14 16 18 20 22 24 26 28

bL

0 (c

m-1

atm

-1) a

t 296

K

0.068

0.072

0.076

0.080

0.084

0.088 Air-Shift Coefficients

J"

14 16 18 20 22 24 26 28

0 (c

m-1

atm

-1) a

t 296

K-0.016

-0.012

-0.008

-0.004

0.000

0.004

3 (Present Work)

33 (Smith et al., 1994)


Summary

• Intensities, air-broadening and shift parameters have been determined for 41 ν3 P-branch lines with J˝ = 15 – 26 from spectra recorded at temperatures from 160 K to 300 K.

• Intensities retrieved with 2005 version of the multispectrum fitting program are identical to those retrieved from the same spectra for the 2001 study.

• Air-broadening coefficients agree within 5% or better with measurements in the ν1, ν2, and 3ν3 bands and with HITRAN 2004.

• Air-shift coefficients agree within error bars with measurements in the ν1 and ν2

bands and with HITRAN 2004.

• Vibrational dependence of the air-shift coefficients is apparent between the ν3 and 3ν3 bands.

• Temperature dependence exponents for air-broadening are 5 to 25% smaller than HITRAN 2004 values. The measured values generally decrease with J˝, while the HITRAN values increase with J˝.

• More research is needed!

Explore. Discover. Understand. AIR-BROADENED LINE WIDTHS AND SHIFTS IN THE ν 3 BAND OF 16 O 3 AT...

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