INTRODUCTION
This proposal seeks to address the impact of changing energy usage on the chemistry of the
troposphere. Exploring the importance of shifting energy usage is timely and central to our understanding
of a host of current as well as future atmospheric processes as both the quantity and quality of energy
sources change. The first objective will be to examine the importance of the rapid increase in fuel ethanol
(CH3CH2OH) production and usage on the chemistry of the atmosphere. The United States and Brazil are
leaders in ethanol production at 15 million gallons per year during 2008 (Fig. 1). The United States has
seen an exponential rise in the production and consumption of ethanol during the past decade (Fig. 2) with
production estimated to reach 20 million gallons per year by 2012, primarily in the Corn Belt (central
Indiana and central Illinois and all of Iowa) (http://www.marketresearchanalyst.com/2008/01/26/worldethanol-production-forecast-2008-2012/).
World Fuel Ethanol Production by Country
9,000
8,000
Production (Million Gallons)
7,000
6,000
5,000
2007
4,000
2008
3,000
Fig. 1. Worldwide production of
CH3CH2OH (millions of gallons) by
country in 2007 and 2008
(http://www.afdc.energy.gov/afdc/data/fu
els.html).
2,000
1,000
ia
th
er
O
Au
st
ra
l
a
ia
In
d
nd
m
bi
lo
Th
ai
la
Co
a
in
Ca
na
da
op
e
Ch
Eu
r
US
A
Br
az
il
0
U.S. Production and Consumption of
Fuel Ethanol
Million Gallons Ethanoll
8,000
7,000
6,000
5,000
Production
4,000
Consumption
3,000
2,000
Fig. 2. Production of CH3CH2OH
(millions of gallons) by year in the
United States
(http://www.afdc.energy.gov/afdc/data/fu
els.html).
1,000
2007
2005
2003
2001
1999
1997
1995
1993
1991
1989
1987
1985
1983
1981
0
www.eere.energy.gov/
afdc/data/index.html
There have been no detailed studies documenting the occurrence and variability of ethanol in
atmospheric waters in North or South America despite its reactivity in the troposphere and the projected
dramatic increase in production and use. The presence of simple alcohols such as ethanol in the gas
phase at both urban and rural locations has been known for several decades where they make up a major
fraction of the oxygenated organic compounds (Warneck, 2006). Quantifying only gas phase ethanol
concentrations and reactivity does not, however, fully elucidate its current or future importance to the
chemistry of the troposphere because its reactivity is so critically dependent on its physical state. To
assess the role of highly water soluble species such as ethanol to the chemistry of the troposphere it is
critical to understand ethanol’s occurrence and processing in the aqueous phase.
Studies of ethanol concentrations in precipitation have been limited primarily by the inadequacy of
existing analytical methods. Saturated straight chain alcohols are difficult to quantify in aqueous
environmental matrices because they are in very low concentrations, structurally similar to water, have
poor molar absorptivities and are hard to derivatize. Available methodologies do not have the required
sensitivity or suffer from very low recoveries (~3%) to measure the analyte at environmentally relevant
concentrations. Our laboratory recently developed a simple and highly sensitive method capable of
1
detecting ethanol at nM levels in the aqueous phase. The analysis is based on oxidation of ethanol by the
enzyme alcohol oxidase which quantitatively produces acetaldehyde. The acetaldehyde reacts with 2,4dinitrophenylhydrazine forming an azide which is separated from interfering substances and quantified by
HPLC. Comparison of initial acetaldehyde concentrations with that after enzymatic oxidation yields the
ethanol concentration. The method has undetectable blanks and a very low limit of detection (25 nM).
This method also provides acetaldehyde concentrations, a product of ethanol oxidation. Analytical details
can be found in the Procedures section.
The goal of the research proposed here is to utilize this new method to quantify ranges and
patterns of variation of ethanol in rainwater thus providing the first comprehensive examination of
ethanol’s occurrence in rain. Concurrent measurements of acetaldehyde and acetic acid will provide
important information on the rates of transformations of ethanol occurring in atmospheric waters as well
add to our continuing long-term study of organic acids at this location (Avery et al., 1991; Avery et al.,
2001; Avery et al., 2006). We propose to investigate the impact of air mass origin as revealed by back
trajectory analysis on ethanol, acetaldehyde and acetic acid concentrations with a particular focus on
storms originating in the Midwest Corn Belt region of the United States where ethanol production and use
is greatest. A preliminary assessment of rainwater concentration data revealed that there was an order of
magnitude more ethanol in a storm originating in the Midwest Corn Belt region relative to a terrestrial
storm originating from the Northeast United with corresponding higher acetic acid concentrations
compared with other terrestrial trajectories (7.0 M versus 2.1 M acetic acid, significant at p = 0.015
based on t test). Based on these preliminary results it is essential to conduct this project now in order to
assess potential atmospheric impacts of dramatic increases in ethanol production and use as fuel in the
US.
A carefully conducted comparison of gas phase ethanol concentrations in Sao Paulo Brazil with
Los Angeles, both extremely large metropolitan areas, revealed gas phase ethanol concentrations 10 to
100 times higher in Brazil where ethanol makes up 40% of vehicle fuel compared with < 3% in Los
Angeles (Colon et al., 2001). The authors attributed the high gas phase ethanol concentrations in Sao
Paulo to evaporative and exhaust emissions from automotive sources. A more recent study in Brazil
hypothesized that ethanol concentrations in rain could be as high as 80 M based on measured gas phase
concentrations and the Henry’s law constant for ethanol (Coelho et al., 2008). Concentrations of ethanol
this high would represent a substantial fraction of rainwater DOC and would significantly impact the
composition of this dynamic and changing component of atmospheric waters. We conducted a calculation
similar to Coelho et al. (2008) based on gas phase ethanol concentrations reported in 2001 for Los
Angeles by Colon et al. (2001). On the basis of these calculations the ethanol concentration would be 3
M, also a contributing fraction of rainwater DOC. Considering the LA gas phase measurements were
made when ethanol production and consumption was 1/7 that of today, it is likely that ethanol
concentrations are significantly higher and that it is contributing much more DOC to rainwater in this area
and the United States in general.
We will conduct this phase of the proposed research in collaboration with Dr. Lúcia Campos at
the Universidade de Sao Paulo, Brazil. After conducting stability tests for transport, we will quantify the
ethanol, acetaldehyde, acetic acid and DOC concentration in rain samples collected in Brazil during the
proposed study (see attached letter of support) in addition to samples collected at the Wilmington site.
This data set will provide direct quantitative evidence for the importance of ethanol usage as a fuel on
aqueous phase alcohol concentrations and DOC levels in precipitation. Comparison of the Brazilian data
to rainwater collected at the Wilmington site will also provide a unique opportunity to examine how
shifting ethanol usage in North America could ultimately impact the chemistry of the troposphere as our
use of ethanol increases.
DOC concentrations have decreased approximately fifty percent in Wilmington rain over the
preceding decade most likely due to the use of reformulated gasoline and other improved pollution
2
control technologies (Fig. 3). A great unknown in the future is potentially increasing anthropogenic
inputs of alcohols, their oxidation products and VOC’s from increasing biofuel usage. Certainly an
increase of anywhere close to 160 M DOC as hypothesized in the Brazil study would dominate
rainwater DOC for our study area. Measurements of rain DOC by our group during the past three years
appear to show a rebound in DOC concentrations with volume weighted average DOC concentrations
approaching the 80-100 M driven by increases in rain with a back trajectory over the Corn Belt.
Rainwater concentration data from 2007 to the present revealed higher DOC concentrations in rain with
storm origin over the Corn Belt compared with other terrestrial trajectories (211 M versus 55 M DOC,
significant at p = 0.005 based on t test), consistent with predictions for rain in Brazil. We hypothesize
that this difference is associated with recent increases in ethanol production and consumption in the
United States which dramatically increased starting in 2003 (Fig. 2). Conversely, rainwater pH values
have leveled off or slightly increased during the past several years consistent with increases in non-acidic
organic species such as ethanol and acetaldehyde. It is important to understand processes causing these
differences in DOC concentrations at the present time.
DOC ( M)
150
Fig. 3. Volume weighted annual averages and standard
deviations for DOC in Wilmington, NC rainwater from
1995 – 2005 (Willey et al., 2006).
100
50
0
1995
2000
2005
Year
Another potential unforeseen consequence to the increase in ethanol use as an energy source is a
corresponding increase in the abundance of volatile organic carbon compounds (VOC’s) in precipitation.
Coelho et al. (2008) recently reported extremely elevated DOC and VOC concentrations in rainwater
from Brazil which the authors attributed to the extensive production and consumption of ethanol as a fuel.
Preliminary data from our laboratory revealed an elevated VOC concentration in one rainwater sample
collected from an air mass back trajectory originating from the Midwest United States with a VOC
concentration of 44 M which was 20% of the total DOC (Avery et al., 2009). One possible explanation
for the high VOC level in this rainwater sample could be aqueous phase oxidation of ethanol to
acetaldehyde. As part of this proposal we will expand this small data set (five rain events) to establish a
comprehensive understanding of VOC’s in rainwater originating from various back trajectories in North
America. Furthermore we will explore the relationship between ethanol and acetaldehyde concentrations
and total VOC’s to determine if there is a link between VOC occurrence and these two compounds that
are likely to dramatically increase in the future.
We hypothesize based on preliminary results from our laboratory and the Brazilian studies that
significant concentrations of ethanol, acetaldehyde and acetic acid exist in rainwater with much variation
between rain events driven primarily by air mass origin and season. We further hypothesize that these
three compounds will make up an increasing fraction of the DOC pool in rainwater and increases in
acetaldehyde will lead to an increase in VOC’s in rainwater. Based on these hypotheses and our
preliminary data we propose the following objective.
Objective 1. Quantify ranges and patterns of variation in the abundance of ethanol, acetaldehyde
and acetic acid in rainwater including the effects of season and air mass origin on concentrations.
Compare concentrations of the various analytes to analogous rainwater samples collected in Brazil.
Investigate the role of ethanol production and consumption on VOC and DOC levels in
precipitation through comparison of rain events of different origins.
3
Increases in ethanol usage, as described above, will have a significant impact on a variety of
fundamentally important atmospheric processes. Recent studies suggest, for example, that reactive uptake
of gas phase ethanol and aldehydes occur in the presence of sulfate aerosols (Iraci and Tolbert, 1997;
Kane and Leu, 2001; Michelsen et al., 2006). The observed uptake is believed to occur through sulfate
esterification where the poly-condensation products formed have different water solubilities and optical
properties. Increases in ethanol usage, along with other mitigating factors such as evolving emission
control technologies, will also cause significant fluctuations in fossil fuel emissions to the atmosphere.
The second phase of the proposed research seeks to explore the importance of changing fossil fuel
emissions on the abundance of light absorbing or chromophoric organic material (CDOM) in rainwater.
Investigating CDOM is important because these molecules play a central role in solar radiative transfer in
the condensed phase affecting both the attenuation and spectral distribution of sunlight reaching the
earth’s surface. They could also have a significant impact on droplet population and cloud albedo by
lowering the surface tension of atmospheric waters (Facchini et al., 2000; Decesari et al., 2005; Kiss et
al., 2005).
The first step in determining the role of fossil fuel emissions on the abundance of CDOM in
atmospheric waters was to determine its stable carbon isotopic composition (expressed as 13C). The
13C values of whole rain DOM ranged from -23.7 to -27.7 ‰ (average -25.7 ± 1.2‰) with storm back
trajectory acting as a key control of inputs from terrestrial(~-27 ‰) to marine (~ -20 ‰) carbon sources.
C18 extracted DOM, in contrast, was highly depleted in 13C compared to whole rain DOC with an
average 13C value of -32.3 ± 1.2 ‰. These values are very light and suggest C18 extracted DOM, which
contains a significant fraction of the chromophoric material (Miller et al., 2009), is not typical biogenic
terrestrial or marine material.
One very interesting hypothesis for the depleted 13C in C18 extracted CDOM compared to
whole rain DOC is that CDOM has a significant fossil fuel component. We have obtained preliminary
evidence supporting this hypothesis utilizing automobile exhaust bubbled though synthetic rainwater
(SRW; pH 4.5 sulfuric acid in deionized water). After ten minutes the resulting mixture contains organic
moieties with optical properties similar to CDOM with an absorbance coefficient at 300 nm (0.29 m-1)
and a total integrated fluorescence (30.5 x 103) very near the average values observed for CDOM in
rainwater (n=120) of 0.37 m-1 and 29.0 x 103 respectively (Kieber et al., 2006). Previous research has
suggested that rainwater CDOM plays a central role in photo mediated reactions occurring in atmospheric
waters because of its photolability even when exposed to short term irradiations with simulated sunlight
(Kieber et al., 2007). Preliminary evidence demonstrates that the fluorescence of car exhaust in SRW
during a six hour irradiation increased to a maximum value during the first two hours followed by steadily
decreasing values. This pattern of fluorescence is remarkably similar to the photolysis of authentic
rainwater (Fig. 4). Preliminary data generated by the latest in accurate mass, high resolution mass
spectrometry utilizing Fourier transform ion cyclotron resonance MS (FT-ICR MS) demonstrate that the
unphotolyzed automobile exhaust and rain water are heterogeneous and complex mixtures with individual
molecular ions between m/z 250 to 800 (Fig. 5).
4
100000
50000
Fig. 4. Entire scan integrated
EEM fluorescence (integrated
Fluorescence
Fluorescence
80000
40000
30000
fluorescence units) of authentic
rain (left) and car exhaust
bubbled through SRW (right)
as a function of irradiation
time.
60000
40000
20000
0
20000
0
2
4
Time (hrs)
6
0
1
2
3
4
Time (hrs)
5
6
Fig. 5. High resolution FT-ICRMS
data from a coastal rain event and
car exhaust bubbled through SRW.
The results presented in Figs. 4 and 5 raise several important questions central to our
understanding of the role of fossil fuel derived organic compounds as a source of CDOM in atmospheric
waters. How do the chemical constituents in fossil fuel derived CDOM compare to those in authentic
rainwater initially and as a function of irradiation time? Are the photo induced compositional
variations for authentic rainwater consistent in all rain events or does air mass back trajectory
and season influence results? Are the photolytic responses reversible?
When the authentic rain sample in Fig. 4 was irradiated with photosynthetically active radiation
(PAR; 400-700 nm) rather than full spectrum sunlight the fluorescence increased steadily throughout the
entire six hr photolysis (Fig. 6 left panel) in contrast to the oscillation in fluorescence observed in Fig. 4.
The pattern of fluorescence increase presented in Fig. 6 implies significant production of highly
chromophoric material from non chromophoric and/or less chromophoric organic moieties in rainwater.
The PAR irradiation study was conducted with a second rain event with similar results suggesting this
was not an anomalous rain sample. The results of Figs. 4 and 6 suggest that not only does light photo
bleach CDOM as previously reported but it also produces significant quantities under certain irradiation
conditions. This proposal seeks to answer the following questions based on these important results.
Do all authentic rainwater samples have the same response to PAR and is the response of fossil
fuel derived chromophoric material to varying exposure wavelengths the same as authentic rainwater?
What are the mechanistic underpinnings and compositional variations causing the oscillations in
fluorescence upon exposure to full spectrum sunlight relative to the rapid increase in fluorescence with
PAR only presented in Fig.6?
Resolving these uncertainties has profound ramifications for predicting how fluctuations in fossil
fuel emissions will impact the wavelength dependent spectral attenuation of sunlight reaching the earth’s
surface and global climate change models. We propose the following objective based on these important
questions.
5
80000
40000
60000
30000
Fluorescence
Fluorescence
Objective 2. Determine the molecular level composition of chromophoric material obtained from
various fossil fuel derived combustion sources and compare with authentic rainwater collected
from different air mass back trajectories and seasons as a function of irradiation time and exposure
wavelength (full spectrum, UV and PAR light). Assess the reversibility of observed optical and
compositional photolytic responses.
40000
20000
Fig. 6. Entire scan integrated
EEM fluorescence (integrated
fluorescence units) as a
function of irradiation time
with PAR for two different
rain samples.
20000
10000
0
0
0
2
4
6
8
0
1
2
Time (hrs)
3
4
5
6
Time (hrs)
An important consequence of the increase in ethanol usage and fluctuating fuel emissions is the
potential to change the redox properties of the troposphere by generating or destroying reactive species
such as hydrogen peroxide. Ethanol may affect the oxidizing capacity of atmospheric waters because of
its potential reactions with H2O2, ∙OH and ∙HO2 radicals in solution that form acetaldehyde and acetic
acid. We have preliminary data utilizing car exhaust bubbled through SRW indicating that significant
concentrations of hydrogen peroxide are produced upon photolysis of fossil fuel derived chromophoric
material (Fig. 7). The maximum concentration in this synthetic solution at 2.5 hrs could account for
approximately half the volume weighted average hydrogen peroxide concentration in rainwater at the
Wilmington collection site between 2001-2003 (Willey et al., 2006) indicating the potential significance
of this process to the abundance of peroxide in the aqueous phase. Production of hydrogen peroxide from
fossil fuel derived CDOM has important implications for the oxidizing and acid generating capacity of the
troposphere because it is a chemically labile oxidant which plays a role in the conversion of a number of
highly reactive free radicals and trace metals as well as its central role in the conversion of sulfur dioxide
to sulfuric acid in cloud and rainwater (Calvert and Stockwell, 1983; Calvert et al., 1985). Because of the
potential importance of this process to the chemistry of the troposphere we propose the following
objective.
H2O2 (M)
6
Fig. 7. Concentration of H2O2 (M) in
fossil fuel derived CDOM as a function of
irradiation time (hrs).
4
2
0
0
1
2
3
4
5
Time (hrs)
Objective 3. Quantify the production of hydrogen peroxide from photolysis of fossil fuel derived
CDOM obtained from various sources. Determine the role of sample matrix and the efficiency or
apparent quantum yield of this photo process.
6
The final objective of the proposed research explores the relationship between fluctuations in
fossil fuel emissions on the speciation of iron in atmospheric waters. Iron is one of the most abundant
trace metals in rainwater, where it occurs in particulate and dissolved forms, including both free and
complexed ferrous and ferric iron species (Willey et al., 2000; Kieber et al., 2001; Kieber et al., 2001).
Iron plays an important role in the redox chemistry of the troposphere because of its involvement in
reactions such as the decomposition and generation of H2O2 in cloudwater (Zuo and Hoigne, 1992;
Sedlack and Hoigne, 1993) and fog (Zuo and Hoigne, 1992; Zuo and Deng, 1999) and the conversion of
S(IV) to S(VI) (Graedel et al., 1985; Jacob et al., 1986; Breytenbach et al., 1994). The oxidizing capacity
of the troposphere is influenced by the reactivity of Fe with several free radicals including OH, HO2, and

O2- (Faust and Hoigne, 1990; Faust and Zepp, 1993; Sedlack and Hoigne, 1993; Siefert and Hoffmann,
1996) and with other redox-active trace metals such as copper and chromium (Erel et al., 1993; Faust and
Zepp, 1993; Zuo, 1995; Abu-Saba et al., 2000; Kieber et al., 2002; Kieber et al., 2004). Rainwater is an
important delivery mechanism for iron to surface seawater where it is a limiting phytoplankton nutrient in
vast regions of the world’s oceans. This delivery of labile Fe is thought to play a significant role in the
removal of carbon dioxide from the atmosphere.
The concentration of Fe(II) in 2008 was less than half its value in 2000 in both winter and
summer rain collected at the Wilmington site (Willey et al., 2009). Rain in the first half of 2009 continues
to be very low in Fe(II) suggesting 2008 was not an anomalous year but rather there may be an ongoing
fundamental change in the speciation of Fe in atmospheric waters. Storage experiments performed on rain
collected during the summer of 2008 revealed significant oxidation of Fe(II) by hydrogen peroxide within
hours in marked contrast to the stability of Fe(II) observed in rain collected five to ten years ago where
there was no decrease in Fe(II) even after 24 hours storage. Recent studies suggest that the decreased
stability and concentration of Fe(II) compared to a decade ago may result from a lowering in the
abundance of iron ligands in rainwater (Willey et al., 2009).
Preliminary data suggest the most effective Fe ligand(s) in rainwater are contained within the
chromophoric dissolved organic matter fraction with higher Fe(II) concentrations in highly fluorescing
samples (Fig. 8). The correlation between Fe(II) and CDOM fluorescence is much stronger than that
between Fe(II) and DOC because about half the compounds in rainwater DOC cannot form complexes
with Fe(II) (ex. formic and acetic acids). The fluorescence of rainwater was not measured a decade ago
so it is unclear if the higher concentrations and greater stability of Fe observed in 2000 were the result of
increased levels of these Fe ligands or if some other factor was controlling Fe speciation.
The relationship between the concentration of Fe(II) and CDOM presented in Fig. 8 raises several
important questions central to the redox chemistry of the troposphere. Is fossil fuel derived chromophoric
material capable of binding Fe(II)? If so, has the amount or complexation capacity of fossil fuel CDOM
decreased due to more effective pollution control technology? How do the photochemical changes in
CDOM caused by exposure to sunlight presented in Figs. 4 and 6 affect the ability of CDOM to bind
Fe(II)? If Fe(II) binds to photochemically mediated and anthropogenic CDOM how easily is it removed?
Does Fe(III) also complex fossil fuel derived CDOM?
100
y = 0.001x - 8.939
Fe(II) (nM)
80
Fig. 8. Fe(II) concentration (nM) versus total integrated
CDOM fluorescence (quinine sulfate units) in rainwater
collected in Wilmington, NC between 1 January and 31
December 2008. n = 52, r = 0.748, p < 0.001.
2
R = 0.559
60
40
20
0
0
20000
40000
60000
80000
integrated fluorescence (QSU)
7
Exploring the significance of changing fossil fuel emissions on the speciation of Fe is especially
important to understanding the role of the metal in current as well as future atmospheric processes.
Unraveling these uncertainties will also have direct and profound consequences for global carbon budgets
and climate warming because lower concentrations of Fe(II) implies there will be less removal of
atmospheric CO2 by marine phytoplankton.
Objective 4. Determine the role of photochemically mediated and fossil fuel derived CDOM on the
speciation and stability of iron in rainwater. Assess whether the concentrations or effectiveness of
CDOM as a ligand for Fe(II) has changed.
Sampling Procedures
Field Sampling: Rainwater will be collected at our existing rain site on the UNCW campus on an event
basis throughout this three-year project. This time period is necessary in order to define seasonal
variations and incorporate extreme weather events like drought and hurricanes. This rainwater site
(34º13.9'N, 77º52.7'W) is on the UNCW campus, approximately 8.5 km from the Atlantic Ocean. We
currently have 24.5 years of rainwater composition data for this site, which will be useful in interpretation
of data generated and also will allow comparison with other locations. Event rain samples will be
collected using four Automatic Wet-Dry Precipitation Collectors. Samples for pH, inorganic ions,
hydrogen peroxide, dissolved organic carbon and CDOM analyses and experiments will be collected from
samplers containing a 2L muffled Pyrex glass beaker. Samples for trace metal analysis will be collected
in collectors containing a HDPE funnel leading to a 1L Teflon bottle extensively cleaned using trace
metal clean procedures and protocols (Bruland et al., 1979; Bruland, 1980; Tramontano et al., 1987).
Back trajectory analysis will be used to describe the storm origin (NOAA HYSPLIT Model
http://www.arl.noaa.gov/ready/hysplit4.html).
Procedures – Objective 1
Ethanol and Acetaldehyde: Acetaldehyde concentrations in rainwater samples will be determined after
reaction with 2,4-dinitrophenylhydrazine (2,4-DNPH) for one hour in the dark forming a hydrazone
which is separated from interfering substances by HPLC and quantified by UV detection at 350 nm
(Kieber et al., 1999). The detection limit of the method is 10 nM with a precision of 5% at typical
rainwater concentrations.
Ethanol will be determined on a second aliquot of rainwater by oxidation of the alcohol to
acetaldehyde via alcohol oxidase obtained from the yeast Hansenula sp. The enzyme is prepared by
dissolution of 100 units of alcohol oxidase in 5 mL of 0.1M potassium phosphate buffer (pH 9.0). The
rain sample (1000 μL) is combined with 10 μL of buffer, 100 μL of an enzyme working reagent (0.18
units mL-1) and allowed to react at 400C for 2.5 hrs before addition of 10 μL of DNPH. The concentration
of ethanol is determined by the difference in acetaldehyde concentration in samples with and without
added enzyme. The percent conversion of ethanol to acetaldehyde is >90% after 2 hrs at environmentally
relevant ethanol concentrations. Blanks, consisting of synthetic rainwater in place of sample, are
undetectable for both acetaldehyde and ethanol. A typical calibration curve is presented in Fig. 9.
8
70
60
Fig. 9. Peak area vs.
concentration of ethanol (M).
R2 = 0.9996
peak area
50
40
30
20
10
0
0
0.25
0.5
0.75
1
ethanol (M)
Acetic Acid: Acetic acid concentrations will be determined using ion exclusion chromatography with a
IonPac ICE-AS1 4x250mm column. The eluent will be 1mM HCl and the regenerant 0.005M
tetrabutylammonium hydroxide.
DOC and VOC: Rainwater organic and inorganic carbon content will be determined with a Shimadzu
TOC 5000 carbon analyzer (Shimadzu, Kyoto, Japan) equipped with an ASI 5000 autosampler (Willey et
al., 2000). The detection limit for this instrument is 5 M C with a relative standard deviation < 3%.
Typical rainwater DOC measurements as usually reported are non-purgeable DOC (NPDOC).
Samples are acidified in this method to pH 2 with 2 M HCl and sparged with carbon dioxide free carrier
gas for 5 min at a flow rate of 125 mL min-1 to remove inorganic carbon prior to injection onto a heated
catalyst bed (0.5% Pt on alumina support, 680°C, regular sensitivity). A nondispersive infrared detector
measures carbon dioxide gas from the combusted organic carbon. The purging step described above also
removes VOC if present in the rain sample. We have modified the method for determining NPDOC to
measure both total carbon (TC) and inorganic carbon (IC) similar to Campos et al. (2007) in order to
assess rainwater VOC content,. Total carbon (TC) will be determined using the same procedure as
NPDOC except the IC removal step will not be performed. Therefore TC will contain NPDOC, IC and
VOC. Inorganic carbon (IC) concentrations will be determined using the Shimadzu TOC 5000 carbon
analyzer inorganic carbon method. An aliquot of the sample will be injected into an acidic solution and
CO2 measured directly on the non dispersive infrared detector bypassing the combustion step. Samples
for NPDOC measurements will not be filtered since any filtration may remove VOC. A previous study
has shown that particulate organic carbon is not a significant in the rain events received at this location so
filtration is not necessary when measuring NPDOC (Willey et al., 2000). The calculation of VOC is then
made using the equation (Avery et al., 2009): VOC = TC – (NPDOC + IC)
Procedures - Objectives 2 and 3
Approach:
Preliminary data from our group suggests there is a genesis and destruction of CDOM and H2O2
upon irradiation that is wavelength dependant. A variety of sources will be sampled and photolyzed in
order to test if alternating fuel sources or emission control technologies produce different molecular level
distributions of CDOM. Rainwater from different back trajectories and seasons will also be sampled and
photolyzed to relate fuel composition to photochemical changes. DOM will be isolated by C18 SPE and
lyophilization. Structural elucidation of the isolated DOM will be carried out using a variety of techniques
including high resolution, accurate mass MS and 1H and 13C nuclear magnetic resonance (NMR) for
chemical characterization. Electrospray ionization is a “soft” technique giving no fragmentation and
single charged molecular ions. Since the FT-ICR MS generates accurate mass data with the highest
resolution, individual molecular formula can be generated and structures proposed. The elemental
compositions generated will be used to make van Krevelen plots which are atomic ratios of H/C vs. O/C
(Stenson et al., 2003; Kujawinski et al., 2004; Altieri et al., 2009). These plots compare elemental
compositions between samples giving information as to the aromaticity and functionalities present.
9
Further chemical characterization of rainwater and fossil fuel derived CDOM will incorporate
more advanced one and two dimensional NMR techniques in combination with chemical modification of
extracts. Two dimensional NMR experiments which incorporate water suppression techniques will
include COSY (for CH-CH connectivity), TOCSY (total correlation of spin systems within a molecule),
HSCQ (H-C correlation), HMBC (long range H-C correlations) and DOSY (diffusion ordered
spectroscopy for molecular size determination). Chemical modification of extracts will provide further
information concerning the chemical nature of rainwater and fossil fuel derived CDOM. The poly
carboxylic acid nature of the CDOM will be explored by converting carboxylic acids to their methyl
esters. Methylation or acetylation of OH’s and NH’s will convert the DOM into a more organic soluble
fraction which will allow for acquisition of spectra in solvents that will not interfere with signals in the
region of water. This will also give further information on the oxygenated component of the DOM, in
particular, its carbohydrate nature. By using a combined approach, structures of the most abundant
species in the DOM will be identified thus giving insights as to molecular level processes.
Exhaust Collection Procedure: Automobile exhaust will be bubbled through synthetic rainwater (SRW
- MQ with a pH adjusted to approximately 4.5 with 5mM H2SO4). One liter of SRW will be divided into
two 500 mL portions and placed into separate 1L glass bottles with ground-glass stoppers. In order to
bubble exhaust, a glass funnel with a 3” opening will be attached to one end of Tygon tubing and the
other end placed into the 1L glass bottle containing SRW. The funnel will be placed at the tailpipe of a
warm car and secured using a ring stand. The ring stand holding the funnel will be adjusted until the
exhaust bubbles out of the tubing and into the SRW. Once the exhaust bubbles freely, it will be allowed
to collect for ten minutes. This will be repeated for the second portion of SRW. This sampling system
has been successfully developed and used by our lab for the collection of the preliminary data. We will
also sample coal and oil fired power plant emissions with the assistance of the NC Department of
Environment and Natural Resources.
CDOM Extraction: C18 SPE cartridges will be preconditioned by washing with 2 X 5 mL 90%
methanol:10% water followed by 2 X 5 mL deionized water. Samples for CDOM extraction will be
filtered and loaded onto C18 cartridges by pulling through under vacuum with a 5-port manifold
connected with a 1 L side-arm flask. The cartridges will be washed with 2 X 5 mL of DIW to remove
residual salts before the bound constituents are eluted with 2 X 3 mL of 90% methanol:10% water eluant.
The extracted material will be eluted from the column into 25 mL round-bottom flasks and concentrated
to dryness under reduced pressure (Buchi Rotavapor, Model RE 111, Switzerland). Remaining traces of
water and methanol will be removed under vacuum (Sargent-Welch Model 1400, Skokie, IL).
Optical Properties: The optical properties used to characterize rainwater CDOM include absorbance and
fluorescence (Kieber et al., 2006). Absorbance scans will be made from 240 to 800 nm using 10 cm
Suprasil cuvettes on a Varian Cary 1E dual-beam spectrophotometer (2 nm slit width). Excitationemission matrix (EEM) fluorescence properties will be determined on a Jobin Yvon SPEX Fluoromax-3
scanning fluorometer equipped with a 150 W Xe arc lamp and a R928P detector.
Photochemical Experiments: Controlled photolysis experiments will be performed using procedures
described in an earlier rainwater photochemical study (Kieber et al., 2003). Two quartz flasks will be
enclosed in aluminum foil to serve as dark controls and four will be left unwrapped and irradiated. The
light-exposed and dark flasks will be placed in a constant temperature water bath and irradiated using a
solar simulator (Spectral Energy solar simulator LH lamp housing with a 1000 watt Xe arc lamp)
equipped with a sun lens diffuser and an AM1 filter to remove wavelengths not found in the solar
spectrum. Light measurements will be made with an Ocean Optics SD2000 spectrophotometer connected
to a fiber optic cable terminated with a CC-UV cosine collector. The system is calibrated with a NIST
traceable tungsten lamp and data is collected with OOIrrad software. Aliquots will be withdrawn at
predetermined time intervals over 1-12 hours for analyte determination (hydrogen peroxide, absorbance,
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fluorescence, DOC). Changes in analyte concentration with time will be used to determine rate constants
obtained on authentic rainwater samples from different seasons and storm types. These will be compared
to analogous automobile and power plant exhaust in SRW in order to evaluate the impact of fossil fuel
and rainwater matrices on photochemical changes. Apparent quantum efficiencies of the photo processes
will be carried out using a monochromatic irradiation system consisting of a 1000 W Xe – Hg lamp
(Spectral Energy Model LH 153) equipped with a high-intensity 0.25 m grating monochromator (Spectral
Energy Corp. model GM 252-20) and a 10 cm sample cell (Kieber et al., 2003). Light will be detected
using an International Light IL1700 radiometer (5V bias off) with a SED033 detector. Quantum
efficiencies will be calculated at different wavelengths (wavelength-dependent quantum yields) to
determine those wavelengths of sunlight which are most effective at initiating photochemical
transformations and to permit modeling of photochemical processes.
High Resolution FT-ICR MS and 1H, 13C NMR Analyses: The DOM isolated by C18 SPE will be
analyzed on a 9.4 T FT-ICR MS at the National High Magnetic Field Laboratory at FSU by Dr. William
Cooper (see letter of support). The instrument conditions will be the same as Stenson et al., (2003).
Molecular formula will be generated using mass calculator software available at Dr. Cooper’s laboratory
at FSU. The 1H and 13C NMR analysis will be analyzed on a Bruker 600MHz NMR at UNCW in the
Dept. Of Chemistry using published techniques (Miller et al., 2009).
Supporting Analyses: Hydrogen peroxide (H2O2) will be determined by a fluorescence decay technique
(Kieber and Helz, 1986; Kieber et al., 2001). Chloride, nitrate and sulfate concentrations will be determined
by suppressed ion chromatography. pH will be determined using low ionic strength buffers and a Ross
electrode. DOC will be determined by high temperature catalytic oxidation using a Shimadzu TOC 5000
total carbon analyzer.
Procedures - Objective 4
Fe(II) Speciation and Stability: Rainwater will be collected mid event and as soon as the rain event
ends. Fe(II) and Fe(III) will be determined by the spectrophotometric ferrozine method using a 1-meter
(Ocean Optics) or 5-meter (World Precision Instruments) liquid waveguide capillary cell (LWCC)
attached to an Ocean Optics SD2000 spectrophotometer which we have used for rainwater for over a
decade (Willey et al., 2000; Kieber et al., 2001). The analysis for Fe(II) will be repeated every half hour
on samples stored at room temperature in the dark. Oxidation rate constants will be determined and
compared with values obtained in this lab previously (Willey et al., 2005; Willey et al., 2009).
Role of CDOM: Solutions of the chloride salts of Fe(II) and Fe(III) will be mixed with fossil fuel and
extracted rainwater CDOM. Hydrogen peroxide will then be added to a final concentration matching the
rainwater matrix. Fe(II) and Fe(III) concentrations will be monitored over time to look for effects of
complexation on oxidation and precipitation of iron. Temporal changes in fossil fuel CDOM will be
assessed by sampling automobile emissions from cars of varying ages to see if the fossil fuel CDOM
amount and complexation capacity has decreased with the implementation of new emission control
technology.
SCIENTIFIC TEAM
Our research team is uniquely qualified to conduct this research. We have expertise in the
photochemistry of rainwater including determination of wavelength specific quantum yields. We have
experience in the isotopic, FTIR, HPLC, GC, mass spectrometry and NMR characterization of organic
matter from a variety of different environmental matrices including rainwater. We also have over 15 years
experience working with metal speciation in rainwater including Fe, Cr, Hg, Mn and Cu and have a
continuous record of hydrogen peroxide and DOC at this site for more than 14 years. Our rainwater team
has been collecting additional supporting data at this site for over 24 years which will allow comparison
with rain collected elsewhere. This team includes an assistant professor, an associate professor and two
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full professors, continuing our tradition of bringing new faculty into this research project. We have the
equipment in place and running, including a solar simulator, a monochromatic irradiation system, 3-D
fluorometer, 400 MHz NMR, IR, MS, FT-IR, GC-MS, HR-MS, trace metal clean labs and a 1 and 5 m
liquid wave guide long path length spectrophotometer. We will obtain a 600 MHz NMR in November
2009. In addition, our laboratory is directly adjacent to the primary rainwater collection site thereby
minimizing speciation changes caused by storage prior to analysis. We provide educational opportunities
for undergraduate and master’s students, postdoctoral fellows and high school students and teachers
through this research, and thereby contribute to the teaching, training and learning mission of the National
Science Foundation especially of students early in their scientific careers. We have a long record of
successful integration of research and education through involvement of students in all of our research
projects. Out involvement with young students in our research recruits and retains students in STEM
areas.
BROADER IMPACTS
Benefits to Society: The proposed research seeks to address fundamental questions within the research
objectives of NSF Atmospheric Chemistry. The data generated will provide significant new information
on the effects of changing patterns of fossil fuel and ethanol use, which may cause large changes in
rainwater dissolved organic carbon amounts and composition. This could also affect trace metal
complexation in rain thereby impacting many atmospheric redox reactions.
Advance Discovery and Understanding While Promoting Teaching, Training, and Learning: The
involvement of young scientists early in their careers is an integral part of these investigators’ research
program. High school students, undergraduates, master’s students, high school teachers and post doctoral
fellows will conduct research together in our laboratory along with new and established faculty members.
The graduate researchers will gain valuable teaching experience by acting as mentors to less experienced
students. We will also have one or two high school science teachers or graduate students in training to
become high school science teachers come and join our research team for a month each summer. These
student teachers will receive academic credit with tuition support for their participation. We will work
with the UNCW Watson School of Education to identify the science teachers in training as we have in the
past (see letter of support attached).
Mentoring of the Postdoctoral Fellow: Our postdoctoral fellow will be carefully mentored throughout
this project. The fellow will be invited to give a research seminar soon after arrival so the whole
Department will be introduced to the fellow. The fellow will be included in all Departmental and
laboratory group social events. The fellow will be a central part of our research group, and will gain
experience supervising undergraduate and master’s students. The fellow will be encouraged to contribute
new ideas to this research. We will give the fellow undergraduate teaching experience, initially through
team teaching to build confidence. The fellow will be encouraged to write scientific articles in peer
reviewed journals and present research at scientific meetings in order to increase the eventual
marketability of the fellow. The fellow will participate in proposal writing to gain experience in this
important activity. Career and new position opportunities will be openly discussed as these arise,
including faculty within our research group and beyond. To date, our research group now has experience
mentoring seven postdoctoral fellows. Two have academic positions here at UNCW, two have research
positions (one at Cambridge University and one at the Oak Ridge National Laboratory), one has gone into
high school teaching and two are still with us.
Broad Dissemination to Enhance Scientific and Technological Understanding: We have established
ties with public radio and will continue to present our research to the general public through interviews.
We have presented research findings at UNCW College Day which is primarily for retired persons, and
through the UNCW Odyssey program. Our research is also presented to elementary and high school
students and the PIs often serve as science project advisors for middle school students. The PIs routinely
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serve as science fair judges and advisors for competitions including Science Olympiad and Ocean Bowl.
NSF funded research conducted in our laboratory has been and will continue to be incorporated into our
undergraduate and graduate courses. For example, some of our undergraduate Environmental Chemistry
course lecture material is from our group’s research. The changing energy sources we propose to study
will be a major part of our lectures on carbon budgets and climate change and it will provide students
with a concrete example of cutting edge research with global significance conducted at UNCW. The
high school teachers who work with us in the summer will take information about the research process as
well as research results back to their high school classrooms, and we will encourage continuing contact
and communication between our research group and these teachers by including them in notices about
student defenses and other relevant seminars.
Broaden Participation of Underrepresented Groups: Since our first NSF grant in 1985, approximately
80 undergraduate students, 40 master’s students and seven postdoctoral fellows have conducted research
in our laboratory; more than half have been from underrepresented groups including women and
minorities. If a qualified student applies from a minority institution, or indicates minority status on the
application, every effort is made to find complete funding for that student, including an assistantship and
full tuition support. NSF support in the past has provided needed flexibility to assist with this goal. Every
minority student is carefully mentored, as are all our students in this program. One co-PI (GBA) has
ongoing collaboration with scientists at Elizabeth City State University, a historically black university in
the UNC system. Our research group has had several graduate students from UNC Pembroke, a
historically Native American university. We currently have one student from Pembroke working on the
rainwater research project. Every member of this research team agrees strongly with the UNCW diversity
report goal to “foster a campus climate of inclusion.”
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