Study of
Download
1 / 74

Solomon Bililign, Department of Physics - PowerPoint PPT Presentation


  • 69 Views
  • Uploaded on

Study of Vibrational Overtone Induced Dissociation of Organic Acids From Biomass Burning - Using Cavity Ring Down Spectroscopic Techniques. Solomon Bililign, Department of Physics. About UNC and NCA&T.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Solomon Bililign, Department of Physics' - valencia-cruz


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

Study of Vibrational Overtone Induced Dissociation of Organic Acids From Biomass Burning - Using Cavity Ring Down Spectroscopic Techniques

Solomon Bililign,

Department of Physics


About unc and nca t
About UNC and NCA&T

  • Chartered in 1789, UNC was the first public university in the United States and the only one to graduate students in the eighteenth century. Today, UNC is a multi-campus university composed of all 16 of North Carolina's public institutions that grant baccalaureate degrees, as well as the NC School of Science and Mathematics, the nation's first public residential high school for gifted students.


NC Agricultural and Technical State University

Description

North Carolina Agricultural & Technical State University is a public, comprehensive, land-grant and "high research activity" university committed to fulfilling its fundamental purposes through exemplary undergraduate and graduate instruction, scholarly and creative research, and effective public service. The University is accredited by the Commission on Colleges of the Southern Association of Colleges and Schools to award bachelor's, master's and doctoral degrees. Since its inception as a land-grant university in 1891, North Carolina A&T has had a rich tradition of leadership and achievement. Those qualities are still evident today.

www.ncat.edu | Explore. Discover. Become.


Facts about isetcsc
FACTS ABOUT ISETCSC

North Carolina A&T State University -Lead

North Carolina State University

University of Minnesota

Fisk University-Tennessee

California State University-Fresno

University of Alaska Southeast

City University of New York

Partner Institutions

Aligned with the

NOAA Office of

Atmospheric Research

MISSION

Train students in NOAA scientific

areas and develop technology and

analysis techniques of global data

sets for improved understanding

of climate and environmental

change

Thirty one scientists and engineers in

seven institutions

Nine Academic

Departments

NCA&T Global warming task force report


ISETCSC INTERDSICIPLINARY RESEARCH THRUSTS

Thrust Area I

Sensor science

and technology

Data

assimilation

Sensor Data

Thrust Area II

Global Observing

systems: numerical

and physical

research

Thrust Area III

Data mining & Fusion

Distributed

architecture

  • Climate prediction

  • Pattern recognition for seasonal hurricane forecasts

Sun photometer

TA-1 Departments

Physics

Chemistry

Oceanography

Electrical Engineering

Chemical Engineering

TA-III-Departments

Mathematics

Computer science

Physics

Electrical engineering

CUNY

TA -II- Departments

Physics

Chemistry

Meteorology

Hydrology

Mathematics

Computational science

Environmental Science

Civil Engineering

Scientific

Environmental

Technology

Development

Fresno

Alaska

Student field experience

ChesapeakeBay

FISK


Thrust Area I

Sensor science,

Sensor technology

A-7

Sensor technology,

Eye safe Lidar, etc.

(CUNY)

A-1

A-2

A-3

A-4

A-5

a) Cavity ring down spectroscopy

b) Negative ion proton transfer

mass spectroscopy

(Bililign, Fiddler)

A-6

A-8

Luminescent Sensors (Assefa, NCA&T).

RC(O)O2 + HO2

reaction branching ratios

(Hasson, Fresno State).


The Research Group

Fiddler

Begashaw

Cochran

www.ncat.edu | Explore. Discover. Become.


What is in the atmosphere
What is in the atmosphere?

  • 1950s: Atmosphere is 99.999% composed of N2, O2, CO2, He, Ar, Ne. All are inert! (no chemistry). O3 in the stratosphere. Trace CH4, N2O

  • 1960s: Recognized that reactive compounds in the atmosphere were important even at extremely low levels.

  • 1970s: Regional air quality becomes a major research topic.

  • 1980s: Global atmospheric chemistry becomes a major research topic.


Emission sources
Emission Sources

Natural (Biogenic/Geogenic)

  • Lightning (NOx) N2 NOx

  • Volcanoes (SO2, aerosols)

  • Oceans

  • Vegetation

    * Highly variable in space and time, influenced by season, T, pH, nutrients…

    Anthropogenic

  • Mobile sources

  • Industry

  • Power generation

  • Agriculture

FIRE

Source: Lecture notes by

Christine Wiedinmyer

NCAR


Example emissions from fires
Example: Emissions from fires

Courtesy of Brian Magi, NOAA GFDL


What is emitted from fires
What is emitted from fires?

Urbanski et al., Wildland Fires and Air Pollution, 2009


Acids emitted in Biomass burning

Source: Veres, P., et al. Journal of Mass Spectrometry, 2008. 274(1-3): p. 48-55.

www.ncat.edu | Explore. Discover. Become.


Global Emission Estimates:

Particles

Andreae and Rosenfeld, Earth Science Reviews, 2008


Atmospheric Abundance

CH3OOH

700

H2

H2O2

500

500

Nitrogen

78%

Ethane

500

CO2

380

NH3

400

N2O

310

HCHO

300

HNO3

300

Ne

SO2

Oxygen

200

CO

NOx

He (5)

100

100

20%

18

others

CH4 (1.8)

Ozon

H2OArgon

1%

30

ppb

ppt

ppm

Image courtesy of Max-Planck-Institut für Meteorologie, Hamburg


Biomass burning why do we care
Biomass burning- Why do we care?

  • Biomass burning is a significant source of atmospheric gases and particles

  • It occurs naturally in wildfires

  • It occurs when people clear forests for agriculture, cooking fuel.

  • Most abundant compounds emitted: water vapor, CO2, CO, and thousands of additional compounds and aerosols.

  • Many of these compounds are poorly characterized due to analytical challenges.

  • One poorly understood, but significant class of Volatile organic compounds (VOC) present in biomass burning is gas-phase organic acids. Theyare extremely difficult to measure because of their adsorptive nature.

  • Accurate measurement of optical properties( single scattering albedo) of aerosols is crucial for quantifying the influence of aerosols on climate in climate models and remote sensing applications

www.ncat.edu | Explore. Discover. Become.


Research activities related to biomass burning in bililign s group
Research activities related to biomass burning in Bililign’s Group

  • Negative Ion proton transfer mass spectrometry to Measure: a) Acidities of gas-phase acids; b) Rate of H-transfer; c) Water cluster characterization.

  • Investigate vibrational overtone initiated photodissociation processes that are significant sources of atmospheric radicals using cavity ring down spectroscopy

  • Measurement of the Henry's law coefficient and first order loss rate of Isocyanic Acid in Water Solutions

  • NEW work: measurement of optical properties of biomass aerosols using cavity ring down spectroscopy

www.ncat.edu | Explore. Discover. Become.


Some important photolysis reactions
Some Important Photolysis Reactions Bililign’s Group

O2 + hn (l < 240 nm)  O + O source of O3 in stratosphere

O3 + hn (l < 340 nm)  O2 + O(1D) source of OH in troposphere

NO2+ hn (l < 420 nm)  NO + O(3P) source of O3 in troposphere

CH2O + hn (l < 330 nm)  H + HCO source of HOx, everywhere

H2O2 + hn (l < 360 nm)  OH + OH source of OH in remote atm.

HONO + hn (l < 400 nm)  OH + NO source of radicals in urban atm.


Interest in oh radical formation
Interest in OH Radical Formation Bililign’s Group

  • Life time 10−9 seconds and a high reactivity

  • The hydroxyl radical is often referred to as the "detergent" of the troposphere and has an important role in eliminating some Greenhouse gases dominant removal mechanism of for large number of volatile organic compounds (VOCs)

  • The rate of reaction with the hydroxyl radical often determines lifetime of many pollutants.

  • Major loss mechanism for methane

www.ncat.edu | Explore. Discover. Become.


THE DRIVING FORCE Bililign’s Group

O2

R’OO•

O3

O2

H2O

NO NO2

R

R’•

R’O•

  • The radiation from the Sun drives several processes in the atmosphere:

  • Retention of short and long-wave radiation.

  • Photo-induced chemistry.

OH•


Atmospheric photochemistry
Atmospheric Photochemistry Bililign’s Group

  • Ozone photolysis (λ<310nm)

  • OH radical formation



λ Bililign’s Group ≤ 698 nm

Relatively strong

vibrational overtone

Activation energy =

168.0 ± 3.4 kJ/mol

+ OH•

+ OH•

Other products

Peractic acid:

K. A. Sahetchian, et al., Symp. Int. Combust. Proc., 1992, 24, 637-643.

www.ncat.edu | Explore. Discover. Become.


Direct overtone photolysis
Direct Overtone Photolysis Bililign’s Group

  • In polyatomic molecules the X-H stretching at considerably higher frequency than other vibrational modes.

  • They dominate the ground electronic vibrational overtone spectrum-uncoupled from other vibrations

  • These modes can have direct excitation from the ground vibrational level to several excited levels (“overtone transitions”).

  • If the vibrational level accessed in this way lies above the dissociation limit, dissociation is followed.


VIBRATIONAL OVERTONE-INDUCED Bililign’s Group

PHOTODISSOCIATION

E = hv

ν = 5

ν = 4

ν = 3

ν = 2

ν = 1

Figure adapted from a diagram by Mark M. Somoza


Cavity Enhanced Spectroscopy Bililign’s Group

O’Keefe and Deacon 1988

  • • Light introduced and detected through a mirror.

  • • Light intensity inside of the optical cavity depends on a number of factors, and can be much smaller or much larger than the incident intensity

  • Allows the measurement of absorption coefficient on an absolute scale

  • • Effective or average path length may be very (very, very) long

    • Limited partly, but not exclusively, by mirror reflectivity

  • • So …. offers potential for very high sensitivity absorption (or extinction) spectroscopy


Beer’s Law (Lambert-Beer Law) Bililign’s Group

dz

I0

I

Light

Source

Detector

L

 Absorption (Extinction) Coefficient

 (cm-1) = NAbs (cm-3)  (cm2)

If  is known, N can be determined absolutely


Theory

Absorber [A] Bililign’s Group

I

THEORY

z

LA

d

The detector receives a series of pulses separated by the roundtrip time t = 2d/c with decreasing power from pulse to pulse.

After one pass through cavity:

  • a is the absorption coefficient

  • After each round trip the pulse power decreases by an additional factor

    T = 1− R− A << 1- Transmission is very small

EBAL-08, Cairo, January 2008


Theory1
THEORY Bililign’s Group

  • After m rounds the power has decreased to:

If the detector time constant is large compared to the pulse width it just detects the envelope of the pulse and records an exponential decay with the decay time

With out a gas a = 0; The decay time will be lengthened to

EBAL-08, Cairo, January 2008


Cavity Ring-Down Bililign’s Group

Absorption (Extinction) Spectroscopy

Define:

Minimum detectable absorption is limited by the reflectivity R, the unavoidable losses A of the resonator and accuracy of measuring to and t1

Minimum detectable absorption =

 R= Reflectivity, L cavity length


What is an Optical Cavity ? Bililign’s Group

“A region bounded by two or more mirrors that are aligned to provide multiple reflections of light waves”

Triangular

Bow-Tie

www.ncat.edu | Explore. Discover. Become.


Stable Optical Resonators Bililign’s Group

R = mirror radius of curvature

d = mirror separation

“g parameter”

Stability condition


Gaussian Beams Bililign’s Group

Most optical beams propagating in free space are almost TEM, field component lie in a plane perpendicular to the direction of propagation

The wave is propagating with a velocity = c. The major variation of the field with z is a term of approximate form: exp(-ikz), with k = wn/c= 2pn/lo. Since lo is quite small for optical frequencies, k is a large number.

If the beam has a finite diameter D the transverse divergence can be approximated by Et/D ;So that the ratio of Ez/Et is very small.

Assuming a solution of the form E(x,y,z) = Eoy(x,y,z) e-ikz and substituting into the wave equation, and after some approximation

is the central equation for Gaussian beams

www.ncat.edu | Explore. Discover. Become.


Transverse Electric Modes (TEM) Bililign’s Group

TEM00

TEM10

TEM20

TEM00

Longitudinal

TEMnm

Transverse

TEM11

 (or )


Conditions
CONDITIONS Bililign’s Group

  • mode matched Laser mode to the fundamental TEM00q resonator mode..

  • Mode of laser in resonance

    With a mode of the cavity

  • The relaxation time of the resonator must be longer than that of excited molecules, i.e. R > 0.9999 and careful alignment.

  • Due to the spectral bandwidth of the laser pulse many fundamental resonator modes within the bandwidth dwR can be excited. Therefore in order to resolve absorption lines the laser bandwidth dwL should be smaller than the absorption width.

EBAL-08, Cairo, January 2008


Resonances Bililign’s Groupin Optical Cavities

Round trip phase shift = 2kd = n.2p

Note: k = 2p/l = w/c

Cavity Transmission

Free Spectral Range (nq+1-nq )

Resonant

Non-resonant

Full Width Half Max

FSR

∆


Limitations on Bililign’s Group0 (effective path length)

“Empty”

Cavity Loss

Mirror

Transmission

Rayleigh

Scattering

Mie

Scattering

Interfering

Absorptions

=

+

+

+

  • Mirror Reflectivity

    • Best achievable is T ≈ 5 ppm

    • Strong function of 

  • Cavity Length

  • Rayleigh scattering

    • Rayliegh-4 !

  • Mie Scattering - Aerosol

    • Also scales steeply with 

    • Aerosol extinction can be large!

  • Interfering absorbers

1-2 specific to CRDS

3-5 common to any direct absorption measurement

but … particularly acute when

min < 10-8 cm-1


RING-DOWN TIME Bililign’s Group

Number density of absorber (molec•cm-3)

I0

Absorption coefficient (cm-1)

Absorption cross section (cm2•molec)

Intensity

Speed of light in air

I0/e

Without sample

With sample

Time


Components of a CRD setup Bililign’s Group

Optical cavity with two highly reflective mirrors (~99.995%)

Translated light intensity into an electronic signal

Positioning mirrors

Photomultiplier

Tube (PMT)

Data

Acquisition

Telescope

Dye Laser

Optical

Isolator

Determines Tau values

Matches the lasers pulse and optical cavity modes.

Pulsed laser source with variable wavelength light.

This protects the laser from back reflection

38


EXPERIMENTAL SETUP Bililign’s Group

Pin

Hole

Wave-

plate

Turning

Mirror

Iris

Polarizer

Lens 1

Lens 2

Nd:YAG

Dye Laser

Sample Flow

HeNe Laser

Pressure

Transducer

Purge Flow

Silver

Turning

Mirrors

Collimator

Turning

Mirror

Optical

Fiber

Ring-down Cavity

Mirror Mount

and Bellows

Fitting

Purge Flow

PMT

Zinc

Lamp

Copper Tubing

Teflon Tubing

PC

Phototube

Detector

UV Cell

Exhaust

Bandpass Filter


Flow system Bililign’s Group

N2

Inline

Filter

Bubbler

MFM

Sample

Ring-down Cell

MFM

UV Cell


CRDS SETUP Bililign’s Group


CONTROL AND DATA ANALYSIS Bililign’s Group


INSTRUMENT SPECIFICATIONS Bililign’s Group

  • Ring-down cavity length: 91 cm

  • Typical ring-down times at 620 nm: ~100 μs

  • Dye laser wavelength accurate to ±0.02 nm against HITRAN

  • The minimum detectable extinction coefficient from taking the limit at τ approaches τ0

    αmin~3.5*10-9 cm-1•Hz-1/2



Quantifying photolysis processes
Quantifying Photolysis Processes Bililign’s Group

Photolysis reaction: AB + hn A + B

Photolysis rates:

  • Photolysis frequency (s-1) J = lF(l) s(l) f(l)dl

  • (other names: photo-dissociation rate coefficient, J-value)


Calculation of photolysis coefficients
CALCULATION OF PHOTOLYSIS COEFFICIENTS Bililign’s Group

J (s-1) = lF(l) s(l) f(l) dl

F(l) = spectral actinic flux, quanta cm-2 s-1 nm-1

 probability of photon near molecule.

s(l) = absorption cross section, cm2 molec-1

 probability that photon is absorbed.

f(l) = photodissociation quantum yield, molec quanta-1

 probability that absorbed photon causes dissociation.


Difficult: must measure absolute change in n (products) and I (photons absorbed)

www.ncat.edu | Explore. Discover. Become.


Spectral irradiance l
Spectral Irradiance, I (photons absorbed)L

Typical light ray striking a thin layer of air in

the atmosphere adapted from Madronich, 1987..


Actinic flux I (photons absorbed)

solar zenith angle

Watts m-2

www.ncat.edu | Explore. Discover. Become.


ABSORPTION CROSS SECTION I (photons absorbed)

J = [σ(λ)•Φ(λ)•I(λ)]dλ

  • Data was collected by flowing diluted and undiluted acetic acid sample, which varied the concentration.

  • The number density of monomeric acetic acid in the UV cell (nUV,M) was calculated from the UV absorbance (A) in each experiment, the known equilibrium constant for dimerization (Keq), and the known absorbance cross sections for acetic acid monomer and dimer at 214 nm.


ABSORPTION CROSS SECTION I (photons absorbed)

J = [σ(λ)•Φ(λ)•I(λ)]dλ

  • Dilution was taken into account…

  • and the cross section was determined.

  • The dimer cross section was assumed to be zero.

nUV

Faux/2

Faux/2

Fsamp+Fdil; nin

nRD

51



CALCULATED CROSS SECTION FOR ACETIC ACID MONOMER UNDILUTED ACTIC ACID RUNS

10-Point Rectangular Smoothed Mean ± 1σ

Mean ± 1σ

Mean

10-Point Smoothed Mean

Maximum cross section:

1.84×10-24 cm2•molecule-1

Integrated cross section:

(5.23±0.73)×10-24 cm2•molecule-1•nm

(1.38±0.19)×10-22 cm2•molecule-1•cm-1


COMPARISON WITH OTHER SYSTEMS UNDILUTED ACTIC ACID RUNS


CONCLUSION UNDILUTED ACTIC ACID RUNS

  • An ultra sensitive CRDS instrument with pressure and temperature monitoring capabilities was built.

  • The instrument was used to measure the fourth O-H overtone absorption cross sections for the acetic acid monomer.

  • The results for the monomer are similar to what has been previously reported for other systems.

  • This measurement aids in quantifying the contribution of overtone induced processes for the fate of the acetic acid in the atmosphere.


Solution Compositions UNDILUTED ACTIC ACID RUNS

Peracetic Acid Mixture

+ + H2O

Hydrogen peroxide Acetic acid Peracetic acid Water(AcOH) (AcOOH, 9%) (H2O)

Aqueous Hydrogen Peroxide

+ H2O

Hydrogen peroxide Water

(5%) (95%)



Peracetic Acid Mixture and Aqueous UNDILUTED PERACTIC

Hydrogen Peroxide

All of the peaks in this region can be attributed to water.


I. Begashaw, et al., UNDILUTED PERACTIC J. Phys. Chem. A2011, 115, 753-761, 10.1021/jp1087338.

S. Brown, et al., J. Phys. Chem. A, 2000, 104, 4976-4983, 10.1021/jp000439d.

Missing

feature

Expected absorption from H2O2 not present.

Peracetic Acid Mixture and Aqueous Hydrogen Peroxide


Further Work for Increasing Sensitivity UNDILUTED PERACTIC

  • Increase the limits of detection

    • Increase the cavity length, causing longer ring-down times

    • Switch the bath gas from N2 to He (decreases Rayleigh scattering)

  • Isolate peracetic acid

    • Oxidizing hydrogen peroxide into oxygen

    • Increasing the pH so that acetic acid is mostly deprotonated and kept from entering the gas phase


Pin UNDILUTED PERACTIC

Hole

Wave-

plate

Turning

Mirror

Iris

Polarizer

Lens 1

Lens 2

Wavemeter

Nd:YAG

Dye Laser

HeNe Laser

Pressure

Transducer

Silver

Turning

Mirrors

Purge Flow

Collimator

Fitting

Turning

Mirror

Optical

Fiber

Ring-down Cavity

Mirror Mount

and Bellows

Purge Flow

PMT

Zinc

Lamp

Copper Tubing

Teflon Tubing

Sample

Flow

PC

Phototube

Detector

UV Cell

Exhaust

Bandpass Filter

Increasing the Cavity Length



AcOH UNDILUTED PERACTIC

?

Absorption “shelf”

missing

Broadband absorption or scattering

Causes:

1. Scattering by particles (Mie)

H2O

Filter was used

Gas density only changed by 0.5% (decreased)

Improved Measurement of the Peracetic Acid Mixture

2. Scattering by gasses (Rayleigh)

The isolation of peracetic acid from other constituents is clearly needed.

3. Incomplete mixing of gases with different refractive

indices


H UNDILUTED PERACTIC 2O2 + Ce4+ + SO42– → O2(g) + Ce3+ + H2SO4

AcOOH + Ce4+ + SO42–→

Expected end point: light blue solution (due to ferroin indicator)

Isolation of Peracetic Acid

+ + H2O

Hydrogen peroxide Acetic acid Peracetic acid Water(H2O2, 6%) (AcOH) (AcOOH, 32%) (H2O)

Actual product: yellow liquid with a white precipitate

  • Reaction too slow to be practical (>5 hrs)

  • Strange precipitate, unknown reaction product

  • Another isolation scheme is needed


Sujeeta singh marc fiddler

NEW work: measurement of optical properties of biomass aerosols using cavity ring down Spectroscopy

Sujeeta Singh, Marc Fiddler

www.ncat.edu | Explore. Discover. Become.


Radiative aerosols using cavity ring down SpectroscopyForcing

Incoming solar ~340 W m-2

1827 – Fourier recognizes atmospheric heat trapping

1860 – Tyndall measures infrared spectra

1896 – Arrhenius estimates doubling of CO2

would increase global temperatures by 5-6 oC

Changes since 1750:

long-lived gases ~ 3 W m-2

ozone ~ 0.4 W m-2

aerosols and clouds ~ -1 W m-2

IPCC, 2007


Many different types of aerosols
Many different types of aerosols aerosols using cavity ring down Spectroscopy

Aerosol Extinction

Extinction:

  • Size distributions

  • Composition (size-dependent)

    Need to determine aerosol optical properties:

    t(l) = optical depth

    wo = single scattering albedo

    P(Q) = phase function or g = asymmetry factor

Single particle scattering Albedo:


Measurement of optical properties extinction
Measurement of optical properties: Extinction aerosols using cavity ring down Spectroscopy

Beer’s Law

Extinction Coefficient

(monodisperse aerosols)

Extinction Efficiency

L = path length, N = number of particles per volume


Figure 3. instrumentation for handling aerosols aerosols using cavity ring down SpectroscopySpindler, C.; Riziq, A. A.; Rudich, Y. (2007). Aerosol Sci. Technol.,41, 1011

www.ncat.edu | Explore. Discover. Become.


Nephelometer measuring light scattering
Nephelometer: Measuring light scattering aerosols using cavity ring down Spectroscopy

The nephelometer is an instrument that measures aerosol light scattering. It detects scattering properties by measuring light scattered by the aerosol and subtracting light scattered by the gas, the walls of the instrument and the background noise in the detector.


NEW AEROSOL RESEARCH FACILITY aerosols using cavity ring down Spectroscopy

www.ncat.edu | Explore. Discover. Become.


Mie scattering theory
Mie Scattering Theory aerosols using cavity ring down Spectroscopy

For spherical particles, given:

Complex index of refraction: n =m + ik

Size parameter: a = 2pr / l

Can compute:

Extinction efficiency Qe(a, n) xpr2

Scattering efficiency Qs(a, n) xpr2

Phase function P(Q, a, n)

or asymmetry factor g(a, n)


Mie Scattering with CRDS aerosols using cavity ring down Spectroscopy

A. Pettersson et al. (2004),J. Aerosol Sci., 35, 995-1011


Thank you
Thank you aerosols using cavity ring down Spectroscopy

www.ncat.edu | Explore. Discover. Become.


ad