| PI |
Project |
Year |
Goals |
Results |
# Pubs |
| Cass, G. |
Experimental investigation
of the evolution of the size and composition distribution of
atmospheric organic aerosols |
2000* |
Fine particulate
compositional characterization |
PUBLICATION 1: Average
ambient fine particulate concentrations have declined; EC, CO,
organics and nitrate are higher in winter; sulfate higher in
summer, sulfate and EC have declined over past 15 years; nitrate
and organics show no marked decline; negative measurement artifact
for nitrate due to volatilization from Teflon filters. Q:Highest
fine mass in winter - is that also highest hospital admissions?
PUBLICATION 2: Urban areas with industrial emission sources
appear to have higher mutagenicities per microgram of organic
carbon with secondary pollutants playing a lesser, if any, role;
if important mutagen-forming reactions occur in the atmosphere
they must occur in cold as well as in warm seasons. |
2 (CAO) |
| Chameides, W. |
Southern Center for the Integrated
Study of Secondary Air Pollutants (SCISSAP) |
2001 |
Elucidation of sources and dynamics
of O3 and PM2.5 ambient air concentrations in Southeastern U.S. |
PUBLICATION 1: Inherent uncertainties
result in differences between observations and models when using
air quality models (AQMs) and suggested that all events making
up spatial distribution of O3 be utilized rather than episodic
events as they provide closer correlations. PUBLICATION 2: Consideration
of a marine boundary layer (MBL) source of particles from H2SO4
nucleation is required to understand aerosol distribution; Aitken
mode particles (20-100 nm) are observed in concentrations greater
than predicted such that an additional and more constant source
other than nucleation (i.e. free troposphere entrainment, horizontal
diffusion or unaccounted ocean source) is apparent; the key
is the highly nonlinear nature of nucleation of H2SO4 - a threshold
value determines onset of nucleation process. |
2 |
| Cohen, B. |
Distribution of H+
and trace metals in ultrafine ambient aerosol |
1999 |
Develop a field method
to measure the number concentration and metal content of acidic
airborne ultrafine particles, and a personal monitor for ultrafne
acid aerosols |
FINAL REPORT: Ultrafine
ambient monitor had 73% deposition efficiency for particles
50 nm and only 40% for <100 nm (particle size distribution
on the detector is correlated with particle size distribution
in air using efficiency (?)); 60% for 28nm and 50% for <20;
higher concentrations of NH4+, SO4-2; and H+ in spring and summer
vs fall and winter; nitrate concentrations very low. |
3(?) |
| Eatough, D. |
Continuous measurement of PM2.5
and associated semi-volatile particulate species |
1999 |
Design real-time ambient mass
sampler (RAMS) to avoid errors in mass determination of PM2.5
due to loss of semi-volatile material (ammonium nitrate, organics)
during sampling or addition of particle-bound water |
FINAL REPORT: Water minimization,
good size selection; good agreement with conventional (denuder)
sampler while RFM sampler has 30-40% loss of volatile mass;
precision improved with change from cellulose portion of filter
to glass fibers PUBLICATION 1: Ambient fine particulate concentrations
(mass)are not well correlated with indoor fine particulate correlations,
however ambient fine mass shows some correlation with soot and
ultrafine particles. PUBLICATION 2: Development of fine particulate
samplers w/ denuders (EM-, PC- and W-Boss); W-Boss has precision
of + 0.8 g/m3, others poor; FRM and TEOM under measure PM2.5
~20%. PUBLICATION 3: Diffusion denuder sampling system (PC-BOSS)
combined with particle concentrator eliminates positive and
negative sampling artifacts observed in FRM; 20% of volatilized
material is ammonium nitrate and 80% fine particulate SVOC;
positive artifact due to gas-phase material adsorption with
99% removal by PC-BOSS; denuder lifetime ~ few months; addition
of Naflon-dryer and TEOM to PC-BOSS is RAMS. |
3 + 9(?) |
| Friedlander, K. |
Morphological and chemical characteristics
of the submicron atmospheric aerosol: implication for standards |
2001 |
To establish the prevalence and
physical properties of ultrafine (<0.1 m) and accumulation
(0.1 to 1.0 m) particles, to determine certain characteristics
of these particles as related to health, to characterize ambient
atmospheric aerosol |
PUBLICATION 1: Evaluation of versatile
aerosol concentration enrichment system (VACES) that enriches
concentrations of ambient coarse, fine and ultrafine particles;
volatile species (e.g. ammonium nitrate) are preserved; results
show no occurrence of particle coagulation; results indicate
that ultrafine particles collected without loss; detailed morphological
examinations indicate ultrafine particles collected without
substantial changes in compactness or denseness. |
1 + 1(?) |
| Hochgreb, S. |
Investigation of the formation
of particulate matter in spark-ignited engines |
|
Develop an experimental database
of PM emissions (mass rate, composition, number and size distribution)
from engines; develop and apply a time-resolved diagnostic for
the measurement of instantaneous PM concentrations; use the
developed database to characterize and quantify the important
processes that control PM formation and oxidation in the engine;
and develop a physical model for the PM formation and oxidation
processes. |
CAO WEB PAGE: At high flow rates
(Re > 60,000 and residence time 0.5 sec) as dilution ratio
increases, cooling increases and HC vapor condensation on existing
particles increases, thereby increasing particle mass with particle
concentration increasing up to a dilution ratio of 15:1 and
then decreasing; at low flow rates (Re < 9,000, residence
time 3.5 sec) dilution ratio does not affect temperature and
hence does not affect condensation rate and as dilution ratio
increases, particle concentration decreases up to 15:1 ratio,
then no longer affected; particle numbers decrease by 4% due
to loss on walls, but mass concentration increases by 16% due
to condensation and absorption; at lean air-fuel ratios (HC
emissions high) PM emissions increase in number and mass; injection
of liquid fuel in cylinder increases PM formation; chemical
analyses ongoing. |
0 |
| Johnston, M. R823980 |
Speciation of volatile and reacting
compounds in particulate matter |
1998 |
Speciation of volatile and reacting
compounds into simple particles by laser desorption ionization
mass spectroscopic method (particles ablated with a high energy-pulsed
laser beam) |
FINAL REPORT: With micron-sized
particles, the surface layer is preferentially analyzed so total
composition of the particle may not be determined correctly
if a concentration gradient exists between the surface layer
and the particle interior; recommend removal of water prior
to analysis by laser desorption ionization to minimize quenching
of marker ions and increase accuracy. PUBLICATION 1: NaCl/KCl
and NaCl/NaNO3 multicomponent aerosols observed behaving consistent
with thermodynamic analysis - as relative humidity(RH) reaches
the theoretical deliquescence point the chemical composition
of solution on particle surface changes gradually with increasing
RH until the particle completes transition to aqueous droplet;
this deliquescence occurs at lower points than theory predicts
- possibly due to cracks or pores on the surface; the (NH4)2SO4/NH4NO3
aerosols differed from thermodynamic predictions showing absorption
of water at low RHs - possibly due to the existence of the particles
as metastable aqueous droplets rather than dry particles. |
11 |
| Johnston, M. R823980 |
Speciation of volatile and reacting
compounds in particulate matter |
1998 |
Speciation of volatile and reacting
compounds into simple particles by laser desorption ionization
mass spectroscopic method (particles ablated with a high energy-pulsed
laser beam) |
PUBLICATION 2: Low laser irradiance
theorized to desorb and ionize only material near the particles'
surface while high laser irradiance ablates a greater fraction
of the sample or the particle's surface and core areas; quantitative
determination of relative amounts of nitrate and chloride could
not be assessed due to large particle-to-particle variations;
the increase in particle size due to addition of ammonium nitrate
layer is less than the resolution of particle sizer (200 nm
increase in the diameter of a 3.5 micron particle); only about
1/4 of the condensation occurs on particles; no accuracy or
precision data provided. PUBLICATION 3: Matrix-Assisted laser
desorption/ionization (MALDI) used to characterize aerosol particles
- liquid and solid; in liquid matrix the analyte theorized to
partition between the particle surface and bulk; in solid matrix
the analyte theorized to absorb on surface and deposit there
after crystallization; particles were of uniform size and composition
during each experiment; salt contamination from the aerosol
generator was evident, there may be solution characteristics
unique to small particles ~2 microns; with solid matrix there
is evidence that minor components preferentially deposit in
surface layer while major components deposit in particle core. |
|
| Johnston, M. R823980 |
Speciation of volatile and reacting
compounds in particulate matter |
1998 |
Speciation of volatile and reacting
compounds into simple particles by laser desorption ionization
mass spectroscopic method (particles ablated with a high energy-pulsed
laser beam) |
PUBLICATION 4: Utilization of
real-time ambient mass monitors allows for sampling and analysis
of particles within a millisecond yielding excellent resolution
of particle-to-particle variations and minimizing analyte alterations/reactions
during sampling; ideally the inlet should have high transmission
efficiency (avoids size bias) but inhibited due: 1) rapid acceleration
of entering air stream causing larger particles to hit walls
and perturbing flow, and 2) rapid expansion of flow in mass
spec source region causing smaller particles to move away from
center of flow stream; ideally inlet should also have high flow
rates but often long capillary tubes - which have low flow rates
- are used to enable particle to attain flow velocity prior
to exiting and those with short tubes although flow rates are
high the particles do not have sufficient time to reach velocity
of the flow; for particle detection and sizing one approach
uses 2 continuous laser beams tracking particles thru vacuum
chamber - particle passes thru first beam and provides start
pulse and after passing thru second stream a stop pulse is generated
both by resultant scattered radiation with the inverse of the
time difference between pulses proportional to particle velocity;
with LDI-MS (laser desorption/ionization with time of flight
mass spec) instantaneous detection and analysis are performed
with the main problem being bulkiness or non-compatibility with
portable usage. |
|
| Johnston, M. R823980 |
Speciation of volatile and reacting
compounds in particulate matter |
1998 |
Speciation of volatile and reacting
compounds into simple particles by laser desorption ionization
mass spectroscopic method (particles ablated with a high energy-pulsed
laser beam) |
PUBLICATION 5: The mass spectra
of single aerosol particles found to vary with humidity in 1
or 3 ways; depending on species: 1) sharp transition between
a "wet"-particle spectrum and a "dry"-particle
spectrum over a narrow humidity range (65-70 %) for sodium and
ammonium chloride, 2) gradual spectral transformation over a
broad humidity range (7 - 70%)for ammonium nitrate, and methanesulfonic
acid, and 3) no spectral change with humidity for ammonium sulfate;
wet particles yield very different spectra from their dry counterparts
and signal quenching in wet particle spectra can be severe in
multi-component aerosol compositions; in mixed compositions
only nitrate and chloride could be unambiguously identified.
PUBLICATION 6: On-line and real-time analysis of particles through
nozzles may have biased results especially surface chemical
characterizations due to condensation of vapors onto particles;
increasing lag time (difference between particle residence time
and fluid residence time) and capillary length increases condensation;
condensation of water vapor is the main source; particle condensation
can be significant even for low vapor concentrations and low
surface accommodations; one possible solution is to dry carrier
gas prior to sampling but this may affect aqueous particle compositions;
with certain industrial sampling the presence of other volatile
species in large amounts may contribute to particle growth as
well. PUBLICATION 7*: Positive ion mass spectra of ultrafine
particles are similar to those of micron size particles although
ultrafine particles may have lower cluster signal intensities,
ultrafine particles produce few (or none) atomic or molecular
negative ions with electron emission occurring instead; positive
ion signal intensities decrease only slightly with decreasing
particle size; a small particle exhibits a higher ion yield
than a large particle due to greater fraction of particle vaporized
and lower probability of positive-negative charge recombination.
(*See Wexler) |
|
| Kinney, P. |
Columbia personal exposure study |
2000 |
Characterize levels of and relationship
among personal, indoor, and outdoor urban air toxics, using
2 high schools - 1 in New York city and the other in Los Angeles,
monitoring of PM2.5 (mass and metal concentrations), VOCs and
aldehydes, field work expected to be completed by the end of
2000 |
Ongoing (Mickey Leland Center) |
6(?) |
| Koutrakis, P. R825336 |
Development and Validation of
a Novel Technique to Measure Ambient Particle Properties: Bound
Water, Mass, Density, and Mean Diameter |
1999 |
Develop and test - in an urban
atmosphere - a continuous mass sampler for determination of
mass, density, mean diameter and bound water |
PUBLICATION 1: In general pressure
drop decreases slightly with particle size from 0.2 to 1.0 microns
for any given pore size and face velocity - indicating pressure
drop (PD) is independent of size in this range; there is a sharp
increase in PD as particle size gets smaller than 0.2 microns;
there is a sharp decrease in PD as particle size gets larger
than 1.0 micron due to impaction; particle deposition on pore
edges (main mechanism for increasing PD with time) increases
with size also overall smaller particles have larger overall
surface area so these effects tend to cancel; PD is inversely
related to the square root of particle density; PD nearly doubles
as humidity decreases (33 - 10%) possibly due to greater deposition
via electrostatic mechanisms; at higher humidities (33 - 40
%)greater PD due to loading of liquid particles; for hygroscopic
particles with humidities from 10 - 50 % PD decreases dramatically;
the increase in PD with particle loading can be used to measure
particle concentration when particle density and size are known.
PUBLICATION 2 (Abstract Only): A Continuous Ambient Mass Monitor
(CAMM) was developed that uses fibrous (Fluoropore®) filter
and compared to FRM that uses Teflon® filter; CAMM uses
filter tape transportation system allowing for several weeks
of sampling - 1 hr periods; CAMM has minimum volatilization
and adsorption artifacts and allows for control of relative
humidity; ambient air in 6 urban cities was sampled; NH4NO3,
NH4SO4, elemental and organic carbon and metal oxides were measured. |
3 + 3(?) |
| Koutrakis, P. R825270 |
Development and Evaluation of
a Novel Sampling Method to Determine the Phase Partitioning
of Semi-Volatile Organic Compounds |
2000 |
Develop and evaluate sampling
method that separates particulate and gas phases of semi-volatile
organic compounds and minimizes reactions during sampling of
collected material with any reactive gases (O3, HNO3, HONO,
and SO2) that might be present |
PUBLICATION 2: Particle losses
due to bounce-off and re-entrainment were minimized with this
high volume inertial impactor; particles were collected on a
polyurethane foam; polyurethane foam is inert and nontoxic;
the sampler can operate for a few hours or for a week or more;
this sampler can be used in exposure and/or source apportionment
studies because it collects lots of particles in a short time;
however for trace organics and biological and toxicological
information long time periods are best; solvent extract volumes
required for particle recovery are smaller than with conventional
fine samplers. |
2 + 2(?) |
| Lippman, M. |
Development of a continuous monitoring
system for PM10 and components of PM2.5 |
2000 |
Develop a PM mass monitor for:
ultrafine particles; PM2.5; PM10; NH4NO3; particle-bound water;
and organic compounds |
FINAL REPORT: The monitor reduces
negative (from volatilization) and positive (from adsorbed water)
artifacts in sampling; has 3 size-fractions: coarse (PM2.5-10),
accumulation mode (PM0.15-2.5), and ultrafine (PM0.15 and smaller);
good precision and efficiency. |
1(?) |
| Ondov, J. R825269 |
Development of a semi-continuous
monitor for determination of trace elements and heavy metals
in ambient aerosol particles |
1999 |
Develop a semi-continuous system
for determining concentrations of various elemental components
of fine particles |
FINAL REPORT: The monitor found
to be accurate multi-element aerosol particle sampler with data
down to a 30-minute resolution scale; collection efficiency
~ 95%. PUBLICATION 1: Monitor developed for collection of particles
from 0.5 to 2.5 microns had an efficiency > 80%; flow rate
is 50 L/min 45 or 60 minutes (FRM is 15.7 L/m3 for 24 hours);
particles collected in a slurry at < 0.1 mL/min and can then
be analyzed via furnace atomic spectrometry or inductively coupled
plasma mass spectrometry. |
1 + 3(?) |
| Ondov, J. R825247 |
Atmospheric fate and dry deposition
of urban soot to Great Waters using a novel, state-of-the-art
particulate tracer |
1999 |
Develop optimum tracer techniques
to investigate behavior and deposition characteristics of soot
particles |
FINAL REPORT: Measurement precision
of + 0.2% for ambient aerosol samples with 1-10 pg of Iridium
(Ir) and a detection limit of 150 fg was obtained using isotope
dilution mass spectrometry; analysis by instrumental neutron
activation analyzers (INAA) resulted in a precision of + 0.5%
and a detection limit of 90 fg; no additional benefit from use
of radiochemical neutron activation analyzers (RNAA); Micro-Orifice
impactors used to determine differences in size distributions
of trace elements and Ir tagged soot particles; the largest
errors in particle size measurement occurred at the stage with
the smallest cut point, growth for certain elements was observed
in fine particles (Selenium - 22.4%, Antimony - 17.8% and Zinc
- 14.0%); differences in growth for Cesium were ambiguous; tracer-induced
Ir concentrations in submicrometer sizes well above background
but size differentiations were difficult to make; iridium concentrations
were well above background levels for particles in the submicrometer
range with daily variations; for particle sizes of 2.4 - 1 m
the background was comparable to the tracer concentrations and
was attributed to resuspension and subsequent agglomeration
of tagged soot particles; observations of particles at a site
downwind showed an 18% growth for submicrometer particles and
a 32% growth for 2.4 m particles; large increase in size of
the 2.4 particles appears to reflect differences in amounts
of resuspended dust; the contribution to the ambient air of
particles 2.5 m or smaller was calculated to be 64 kg per year
from diesel trucks (tagged soot); the largest contribution to
tagged soot mass are particles larger than 4.7 m; IR tracer
particles from diesel engines; particle size differences in
site downwind from another attributed to inhomogenieties in
aerosol plume and differences in levels of resuspended dust;
particles were traced to area steel mill, incinerator, coal-fired
power plants and more remote Ohio River Valley area through
size and metal content; the highest concentrations of Fe, Zn,
Cs, Sb and Se associated with steel production; incineration
and coal combustion observed at industrial site; short-term
PM mass and metal compositions found to be spatially non- |
1 + 6(?) |
| Reynolds, S. |
Indoor air quality in large office
buildings in the Midwest |
1999 |
To characterize indoor air quality
and compare (simultaneous measurements) to outdoor air, specific
parameters include CO, CO2, organics, particulates and microorganisms,
psychological (perception) analyses also done |
FINAL REPORT: CO2 values within
range associated with "non=problem" buildings; typical
CO2 values of 1 ppm with highest indoor value of 6 ppm and highest
outdoor value of 26 ppm; no statistical difference observed
between seasons; statistical difference observed between buildings
except for CO2; highest value for themophilic bacteria 66 CFU/m3;
PM10 values ranged from 3-71 g/m3; significant relationships
between exposure to environmental pollutants and adverse health
symptoms reported most prominent for males. PUBLICATION 1: Limonene
(semivolatile terpenoid) shown to be a better indicator of environmental
air quality (than esters, carbonyls, aliphatic and aromatic
hydrocarbons) statistically; limonene was positively correlated
with health symptoms; indoor limonene levels significantly higher
in winter; indoor limonene from perfumes, cosmetics, beverages,
fruits and cleaning agents; states in study (6 buildings) were
Iowa, Minnesota and Nebraska; average indoor concentrations
of limonene ~0.5 ppbv. |
1 + 2(?) |
| Sarofim, A. |
Markers for emissions from combustion
sources |
1997 |
Develop methods for quantifying
the structure and elemental composition of soot to determine
potential use as signature for source of particulate carbon
in ambient air |
FINAL REPORT: No PO listed, no
final report. PUBLICATION 1: High-resolution transmission electron
microscopy (HRTEM) analyzed as potential tool to determine carbon
soot morphology and variations in reactivity with changes in
conversion percentage; this study showed decrease in reactivity
with increasing fractional coverage or conversion whereas an
earlier study found the opposite; the unclear issues identified
were concentration of inorganic material in soot and number
of edge versus face carbon sites. PUBLICATION 2: HRTEM with
correct band filtering (software manipulation via SEMPER6P®)
of the Fourier transform was necessary to obtain realistic parameter
values while eliminating noise and retaining all possible interplanar
spacings; the optimum intensity threshold value must be found
for consistent analyses with particles of various thickness;
quantifiable parameters are circularity, elongation, lateral
extent, angular dependence or fringe orientation, interplanar
spacing and fractional coverage. PUBLICATION 3: Examination
of 3 types of soot from diesel engines used in mining - Idle,
Medium and Heavy; the lateral extent mean value of fringes in
Medium load was slightly less than the other 2; Interlayer spacings
showed the most variation with Idle (4.2 ), Medium 94.6 ) and
Heavy (3.9 ); Medium also had the largest number of fringes
(486) than either Idle of Heavy (301 and 366 respectively);
reasons for difference among soot not clear. |
3 |
| Saxena, V. |
Surface levels of ultraviolet-B
radiation under variable conditions of tropospheric air quality
and cloudiness |
2000 |
Measure UV-B irradiance, characterize
the physical-chemical properties of transported aerosol, digitize
cloud cover, evaluate impact of aerosols, cloud cover and solar
zenith angle on tropospheric UV-B transmission and determine
differences relative to clean and polluted air. |
PUBLICATION 1: Clouds can substantially
reduce incoming UV-B radiation; reflection of radiation occurs
and can increase radiation levels even on cloudy days when radiation
exposure might be deemed to be negligible, however still less
than if no clouds were present. PUBLICATION 2: A single-scattering-separate-delta-Eddington
model was developed that handles both absorption in the stratosphere
and anisotropic scattering within optically thin cloud layers
better than conventional Eddington models and is easier to use;
this method allows for determination of when scattering is important
and when conventional model is good approximation (adequate
for optically thin molecular scattering layers without strong
absorption and for cloud or aerosol layers with optical depths
> 10); this model also enables study of coupling between
scattering and absorption within compositionally complex atmospheric
layers. PUBLICATION 3: A dip occurs in the normalized transmission
at wavelengths < 320 nm (due to coupling of multiple scattering
by aerosol particles and absorption by O3 and to rapidly increasing
absorption coefficient of tropospheric water-soluble particles);
important to note that the combination of aerosols and O3 results
in greater decrease in UV than a simple sum of separate influences;
there is an increase in normalized atmospheric transmission
at wavelengths > 320 nm which implies that the radiative
properties of aerosols cannot be assumed constant in the visible
band of spectrum; depending on humidity levels urban aerosols
reduce transmissions. |
6+ 8(?) |
| Saxena, V. |
Surface levels of ultraviolet-B
radiation under variable conditions of tropospheric air quality
and cloudiness |
2000 |
Measure UV-B irradiance, characterize
the physical-chemical properties of transported aerosol, digitize
cloud cover, evaluate impact of aerosols, cloud cover and solar
zenith angle on tropospheric UV-B transmission and determine
differences relative to clean and polluted air. |
PUBLICATION 4: No substantial
change in aerosol optical depth noted in the past 30 years comparing
this data with previous; differences in optical depth shown
in air masses from highly polluted versus polluted marine versus
polluted continental source regions; highly polluted air masses
showed lowest mean UV-B transmissions; empirical relationships
developed for optical depth and UV-B transmissions; aerosol
single scatter albedo varied greatly with a heavier dependence
on humidity than air mass type. PUBLICATION 5: Black carbon
(BC) mass concentrations averaged 217 ng/m3 in polluted air,
170 ng/m3 in continental air, and 66 ng/m3 in marine air; higher
average BC mass concentrations associated with higher influences
from polluted and continental air masses; BC and cloud condensation
nuclei (CCN) showed positive correlation suggesting a percentage
of BC may be in form of internal mixture; the amount of BC measured
in cloud water too low to significantly effect absorption of
solar radiation by clouds; the amount of BC incorporated in
cloud droplets is small fraction of total; the observed BC/sulfate
ratios will only slightly reduce negative direct forcing by
sulfate. |
|
| Saxena, V. |
Surface levels of ultraviolet-B
radiation under variable conditions of tropospheric air quality
and cloudiness |
2000 |
Measure UV-B irradiance, characterize
the physical-chemical properties of transported aerosol, digitize
cloud cover, evaluate impact of aerosols, cloud cover and solar
zenith angle on tropospheric UV-B transmission and determine
differences relative to clean and polluted air. |
PUBLICATION 6: When clouds are
superimposed on aerosol profile with cloud drops and particles
externally mixed the normalized transmission spectrum is dominated
by effect of cloud drops; the influence of aerosols in external
mixtures decreases with increasing optical cloud depth; when
cloud drops and particles are internally mixed through coagulation
the normalized transmission spectrum is still dominated by cloud
drop effects unless there is an unrealistically high volume
fraction of soot but the influence of aerosols increases with
increasing optical cloud depth; the number density or optical
depth of aerosol particles has a higher influence on magnitude
and shape of transmission spectrum than variations in interstitial
optical depth or volume fraction of absorbing inclusions; in
continental and urban areas prone to high aerosol loadings the
attenuation of clouds with optical depths of 10 or less may
either increase or decrease with wavelength depending on atmospheric
conditions. |
|
| Smith, K. |
Real-time analysis of PAH bound
to size-resolved atmospheric particles by tandem time of flight
mass spectrometers |
2000 |
Develop and demonstrate an aerosol
mass spectrometer capable of quantifying polycyclic aromatic
hydrocarbons (PAHs) associated with individual size-segregated
atmospheric particles in real time |
PUBLICATION 1: For aerosols containing
volatile and semivolatile species, the aerosol mass spectrometer
developed provides good quantitative data on particle size as
a function of chemical composition; aerodynamic particle diameter
is determined by measuring particle velocity via time of flight
(TOF); fast particle detection is through flash vaporization
of volatile and semivolatile components; collection efficiency
is ~ 100% for aerodynamic diameters from 70 - 500 nm; spherical
and/or larger particles focused more efficiently than non-spherical
and/or smaller particles; particles with insufficient mass (<
~2 x 10-14 gm) cannot be detected without averaging mass spec
ion signals over many TOF periods; this method tested for pure
compounds and tests must be run for multi-component compounds;
measurement of mass loading as a function of aerodynamic diameter
can provide more in depth and faster information than FRM; particle
composition information is limited to size-resolved analyses
of particle ensembles. |
1 +1(?) |
| Weisel, C. |
EOHSI personal exposure study |
2000 |
Show relationship between personal
exposure to air toxics and outdoor sources, 3 cities: Los Angeles,
CA(mostly mobile sources); Houston, TX (mostly industrial point
sources); and Elizabeth, NJ(mostly area and point sources) ,
100 homes in each city with ambient and personal monitors, monitoring
for: PM2.5 (mass and metals); VOCs and aldehydes |
Field work done by 2/01, sample
analyses done by 5/01. (Ongoing) Mickey Leland Center |
? |
| Wexler, A. |
Real-time measurement of the size
and composition of atmospheric particulate matter |
2000 |
Development and evaluation of
a portable monitor that sizes and analyzes particles in the
10 nanometer to 2 micrometer range |
PUBLICATION 1: The mass flow rate
of particles exclusively depends upon a modified Reynolds number;
one-dimensional models are adequate for approximating mass flow
through sonic nozzles; beams produced by capillaries have lower
angular spread than those by conical nozzles; in conical nozzles
the beams have a sharp focal point downstream where the beam
width is minimum and beams diverge sharply after focal point;
in capillaries the focal point occurs within the capillary and
beams subsequently straighten out; the particle size distribution
in beams from conical nozzles varies sharply for different axial
locations but not in capillary beams; although capillaries result
in beams of low divergence they: allow lower flow rates, lower
the radial acceleration near nozzle entrance, have increased
nozzle clogging due to inertial deposition of particles on walls,
and promote vapor condensation of particles; for nozzles of
fixed geometry and operating conditions only particles in a
narrow size range are efficiently transmitted hence changing
geometry and conditions allows different sizes of particles
to be sampled. PUBLICATION 2*: Positive ion mass spectra of
ultrafine particles are similar to those of micron size particles
although ultrafine particles may have lower cluster signal intensities;
ultrafine particles produce few (or none) atomic or molecular
negative ions with electron emission occurring instead; positive
ion signal intensities decrease only slightly with decreasing
particle size; a small particle exhibits a higher ion yield
than a large particle due to greater fraction of particle vaporized
and lower probability of positive-negative charge recombination.
(*See Johnston) PUBLICATION 3: A novel technique for rapid analysis
of particles from 1 m to 10 nm was developed; particles are
selectively (by size) transmitted via high speed particle beams
by varying nozzle pressure; as pressure goes from 760 to 3 torr,
optimal particle size goes from 1.8 m to 35 nm; some concerns
with negative ion spectra (dominated by free electrons); modifications
can be made to achieve 10 m upper limit; efficiency is lowered
by deflection by electric field formed by ion optics. |
2 + 1(?) |
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