Trees, Volatile Organic Compounds, and Fine
Organic Aerosol Formation: Implications for Air
Quality, Climate and Public Health in the
Southeastern U.S.
Jason D. Surratt
Department of Environmental Sciences and Engineering, Gillings School of
Global Public Health
Air Quality Concerns in a Changing Climate: Professional Development
Workshop for Teachers
Saturday, September 13, 2014
Who is Jason Surratt?
• Assistant Professor of Atmospheric and Aerosol Chemistry, began at UNC July 2010
• Born in Memphis, TN, and grew up in NC
• Education:
2010, California Institute of Technology (Caltech), Ph.D., Chemistry
Thesis Title: “Analysis of the Chemical Composition of Atmospheric Organic
Aerosols by Mass Spectrometry”
2003, North Carolina State University (NCSU), B.A., Chemistry
2003, North Carolina State University (NCSU), B.S., Meteorology
• Teach a graduate course entitled Aerosol Physics & Chemistry (ENVR 416, Fall)
Teach an undergraduate course entitled Environmental Chemistry (ENVR 403, Spring)
• Research Focus: Directs a “smog” chamber research group in order to understand the
detailed atmospheric chemical mechanisms that cause organic aerosol formation in the
Earth’s atmosphere; we compare our experimental results with field measurements to
gain insights into adverse impacts on air quality, climate, and human health
What Does “Typical” Smog Look Like?
Downtown LA during
a Photochemical Smog Event
Does anyone know which words “smog”
originated from?
Ingredients for SMOG:
Volatile Organic Compounds (VOCs) + Nitrogen Oxides (NOx = NO + NO2) + Sulfur Dioxide (SO2)
+ Sunlight (hν)  “SMOG” (which contains both “bad” O3 and fine aerosol [PM2.5] particles)
How Do We Study Smog & Thus Aerosol?
Same NOx and
VOCs
Same NOx and
VOCs
Wet Experiments
(RH 90%-50%)
Dry Experiments
(RH 40%-10%)
UNC 274 m3 Dual Outdoor Smog Chamber – Pittsboro, NC
Caltech 28 m3 Dual Indoor Smog Chamber
UNC 10 m3 Indoor Smog Chamber Located in MHRC 0016 (Surratt Lab)
Acknowledgements
UNC Surratt Group
Dr. Ying-Hsuan Lin
Dr. Theran Riedel
Dr. Matthieu Riva
Sri Hapsari Budisulistiorini
Tianqu Cui
Weruka Rattanavaraha
Xinxin Li
UNC Gold Group
Prof. Avram Gold
Dr. Zhenfa Zhang
Towson University
Prof. Kathryn Kautzman
University of Washington
Prof. Joel Thornton
Dr. Cassandra Gaston
U.S. EPA
Dr. Havala Pye
Columbia University
Prof. Faye McNeill
ARA, Inc.
Dr. Karsten Baumann
Eric Edgerton
Aerodyne, Inc.
Dr. John Jayne
Dr. Manjula Canagaratna
Dr. Philip Croteau
TVA
Dr. Solomon Bairai
Dr. Roger Tanner
Dr. Stephen Mueller
William Hicks
SOAS Collaborators
Russell & Bertram Groups (UCSD)
Cappa Group (UCD)
McKinney Group (Amherst/Harvard)
Funding
83540401
What are Atmospheric Aerosol?
• Liquid or solid particles suspended in air
• Aerosol = Particles = Particulate Matter (PM)
• PMx: particles with diameters ≤ x mm
PM2.5 : Fine Aerosol
Mass Concentrations regulated by EPA
PM10 : Coarse Aerosol
• Size of Atmospheric Aerosol versus Commonly Known Things:
PM2.5
PM10
Kaiser, Science (2005)
Why Study Atmospheric Aerosol?
• Component of Photochemical Smog & Visibility Degradation
Smoggy Day
Clear Day
VOCs + h+ NOx+ SO2+ O3 + PM2.5
Charlotte,
http://www.southernenvironment.org/cases/southern_air_smog
NC
Charlotte,
NC
What is the chemical
composition (and thus, source)
of this PM2.5?
Why Study Atmospheric Aerosol?
• Role in Global Climate Change:
[Zahardis et al., 2011, Anal. Chem.]
Intergovernmental Panel on Climate Change (IPCC), 2013
Why Study Atmospheric Aerosol?
• Health Effects of PM2.5:
nasal cavity
[Dockery et al.,1993] – Cited 3,477 times
alveoli
Respiratory system
Each 10 mg/m3 increase in PM2.5 long-term exposure has been associated with ~ a 4%, 6%,
and 8% increased risk of all-cause, cardiopulmonary, and lung cancer mortality, respectively.
[Pope III et al., 2006, JAMA]
National Ambient Air Quality Standards
(NAAQS)
NOTE: PM2.5 24 hr is now 35 mg m-3
U.S. Regional Differences in Health Effects
Due To Aerosol Exposures
Dominici et al. [2006, JAMA]
As a Chemist, I ask: What about the chemical compositions might be causing these differences?
Typical Fine Particulate Matter (PM2.5)
Composition
Sulfate
Nitrate
Inorganics
Ammonium
Organics
Aerosol composition from Duke Forest, NC.
(9/13/2004-9/21/2004)
[Zhang et al., GRL, 2007]
complex mixture of
thousands of individual
organic compounds
Organic Material Contributes Significantly to
PM2.5 Mass Across the Globe!
Organic Sources = Primary + SECONDARY
[Zhang et al., 2007, GRL]
Most of Organic Mass!
Types of Organic Aerosol (OA)
• Primary organic aerosols (POA)
• Directly emitted from the sources
• Examples: Diesel soot, wild fire, cooking particles
• Secondary organic aerosols (SOA)
• Formed as a result of atmospheric reactions
• SOA precursors: volatile organic compounds (VOCs)
• Biogenic emissions
• Examples:
isoprene
a-pinene
• Anthropogenic emissions
• Examples:
toluene
naphthalene
“Traditional” View of Secondary Organic Aerosol
(SOA) Formation
(VOCs)
VOCs Known to Yield SOA:
Isoprene
Monterpenes (C10H16)
a-pinene
Sesquiterpenes (C15H24)
-caryophyllene
This Process is Parameterized by Laboratory Chamber Experiments
SOA Yield = Mo/VOC
Mo= organic mass produced (mg/m)
VOC = mass of reacted VOC (mg/m3)
What is the Current Motivation For Studying
Secondary Organic Aerosol?
• Field Studies Indicate HIGHER SOA Formation in the Atmosphere than Models Predict
SOAmeas /SOAmod >> 1
Volkamer et al., GRL (2006)
• Possible Explanations For Discrepancy:
– Other Unidentified SOA Precursors
– Chemical Formation Mechanisms Not Fully Established or Identified
– Role of Aerosol Acidity & Heterogeneous Chemistry
– Chemical Conditions in Laboratory Chambers Not Same as in Troposphere
IMPACT of Aerosols on Climate & Health Cannot be Fully Assessed!
Global Isoprene Emissions
• Isoprene is the most abundant
non-methane hydrocarbon in the
atmosphere
• Observe global distribution of
isoprene in January and July
• What factor(s) might be
responsible for varying distribution
of isoprene over space and time?
•Why do you think the
Southeastern US has elevated
isoprene levels in July?
Guenther et al., ACP (2006)
Global Isoprene Emissions
Guenther et al., ACP (2006)
The yearly production of isoprene emissions by vegetation is around 600 million tons!
• Previously thought not to yield SOA due to high volatility of its known oxidation products
[Pandis et al., 1991, Atmospheric Environment]
• Question of how isoprene oxidation yields SOA re-opened by detection of molecular tracers in
Amazonian PM2.5 [Claeys et al., 2004, Science]
My Current Work: Do the Interactions Between Human
Activities and Natural VOC Emissions Enhance Secondary
Organic Aerosol Formation in S.E. USA?
Biogenic emissions only
Modeled biogenic SOA
Total emissions
(biogenic + anthropogenic)
When all anthropogenic emissions were removed, secondary organic
aerosol (SOA) formation from natural emissions is reduced by more
than 50% or ∼1 µg m-3 in the eastern U.S.
[Carlton et al., 2010, ES&T]
Notably, this interaction could be more pronounced than currently understood
since models currently under predict PM2.5 mass concentrations in eastern USA
Isoprene-Derived Epoxides Are Critical in SOA
Formation from Isoprene Oxidation
[Paulot et al., 2009, Science; Surratt et al., 2010, PNAS; Lin et al., 2012, ES&T;
Zhang et al., 2012, ACP; Lin et al., 2013, ACP; Lin et al., 2013, PNAS;
Nguyen et al., 2014, ACP; Jacobs et al., 2014, ACP]
Implications & Conclusions
• IEPOX-derived epoxides appears to be major source (~1/3) of fine organic
aerosol mass in both rural and urban areas of S.E. U.S. during summer
• Brown carbon from IEPOX occurs in the laboratory due to light-absorbing
oligomer formation; results from field suggest some could be there but
further work is needed to determine how important (abundant) in order to fully
assess impact on radiative budgets.
• IEPOX-derived SOA appears to yield potential inflammation and oxidative
stress in human bronchial epithelial cells; more work is underway
systematically examining gene arrays and investigating individual SOA
components
• Importantly, further reductions in sulfate (SO2) emissions will likely decrease
the amount of fine organic aerosol from isoprene in the S.E. USA region