Why do we care about secondary o rganic aerosol (SOA)?

1. Why do we care about secondary organic aerosol (SOA)? Atmospheric pollutant that can harm human respiratory health Contributes to climate change • Direct effect: aerosols scatter and absorb sunlight, which alters global temperature • Indirect effect: aerosols form clouds, which also scatter sunlight and create more precipitation Production, storage, and use of fossil fuels is a large anthropogenic source of SOA formation[1] Study formation and interactions in the atmosphere in order to mitigate further damage to the Earth’s climate and human health MBO 2-methyl-3-buten-2-ol (MBO) is a biogenic VOC emitted by certain pine species in Western North America Its oxidation has been previously researched[2], so we studied it to check our experimental methods Oxidation of MBO; A product of MBO oxidation is acetone, so monitoring the rate of acetone formation can be used to determine the rate of MBO oxidation Research Goals 1 and 2 Motivation VOC Oxidation Makes SOA Chamber • Chamber is housed in a wooden box (4 ft. x 4 ft. x 6 ft.) • Inside box is a 30 L Teflon bag • The bag can be: • Filled with synthetic air using air-tight tubing • Injected with a VOC using syringe • Vacuumed empty (vacuum pictured to the left) • Chamber is equipped with black lights that provide the wavelengths to simulate solar radiation Proton Transfer Reaction Mass Spectrometer (PTR-MS) PTR-MS tracks the formation of products as the VOC is oxidized We monitor the rate of oxidation product formation in the chamber to estimate the oxidation rate in the atmosphere PTR-MS allows numerous VOCs to be monitored simultaneously with a high sensitivity and rapid response time How does it work?[1] • The air to be analyzed is continuously pumped through a drift tube reactor • A fraction of the VOCis ionized in the proton-transfer reactions with the hydronium ion (H3O+) VOC + H3O+ H-VOC+ + H2O MBO reacts with H3O+ in the drift tube reactor to form the fragments above with mass to charge ratio (m/z) of 87 and 69. These fragments are led through the quadrupoles and their signals are measured Instrument consists of: • A discharge ion source to produce the H3O+ions • A drift-tube reaction, where the proton-transfer reactions between H3O+ and VOC occurs • A quadrupole mass spectrometer for the detection of reagent and product ions Instrumentation Method Development Results Oxidizing Agents • HONO: Created using 10 wt.% H2SO4 and 1 wt.% NaNO2 (see equation on first panel) • H2O2: We expected H2O2 2OH, but this did not occur • H2O2 has a lower absorption cross section at the 350 nm wavelength our blacklights produce, which means it needs more light to photolyze. We need to increase the intensity of our lights Formaldehyde (HCHO), a byproduct in the oxidation of most VOCs; concentration (on the y-axis) increases with both oxidants—meaning MBO oxidation did occur—however formaldehyde oxidizes an order of magnitude faster when reacting with HONO rather than when reacting with H2O2 Injection • We used a 0.5μL syringe to inject given VOC into the Teflon bag • Hole created from injection covered with Teflon tape to prevent air loss and contamination Summary Of Methods Fill empty bag with synthetic air. Use PTR-MS to sample contents of clean bag (should be low concentrations of VOCs) Inject MBO using syringe. Cover hole with tape. Shake bag for about 1 minute to allow compound to fill bag homogenously Use PTR-MS to sample bag to check initial MBO concentrations (specifically watching m/z= 69) Add HONO reagents using glass sample flow cell (see image on next panel) • Charge glassware with 0.75 mL of H2SO4 • Cover top with rubber septum • Inject NaNO2 (drop-wise) into glassware • Lightly flow synthetic air through flow cell to carry sample into the chamber Continue to sample bag with PTR-MS to monitor interactions Turn on black lights Monitor oxidation with PTR-MS Current Work ISOPOOH Currently trying to establish method for quantitatively reproducible ISOPOOH injection Methods of Trial: • Injecting ISOPOOH in the same manner as with MBO • Flowing into the bag with synthetic air • Heating while in the addition glassware and then flowing it into the bag with synthetic air Obstacles: • Scarce ISOPOOH samples to use • Greater viscosity/density of ISOPOOH than MBO • Lower volatility of ISOPOOH than MBO • Sample may be degrading (losing a water molecule) in the time between synthesis and injection de Gouw J, Warneke C. 2006. MEASUREMENTS OF VOLATILE ORGANIC COMPOUNDS IN THE EARTH’S ATMOSPHERE USING PROTON-TRANSFER-REACTION MASS SPECTROMETRY. Wiley Periodicals. 26:223-257 Carrasco N, et al. 2007. SIMULATION CHAMBER STUDIES OF THE ATMOSPHERIC OXIDATION OF 2-METHYL-3-BUTEN-2-OL: REACTION WITH HYDROXYL RADICALS AND OZONE UNDER A VARIETY OF CONDITION. J Atmos Chem. 56:33-55 Lin Y, et al. 2012. ISOPRENE EPOXYDIOLS AS PRECURSORS TO SECONDARY ORGANIC AEROSOL FORMATION: ACID-CATALYZED REACTIVE UPTAKE STUDIES WITH AUTHENTIC COMPOUNDS. Environmental Science & Technology. 46: 250-258 Turco: Earth Under Seige; www.earthobservatory.nasa.gov This research was funded by the Nation Science Foundation under grant #144PRJ45IZ The oxidation of volatile organic compounds (VOCs) contributes to the formation of SOA • VOCs can be biogenic (e.g. emitted by trees) or anthropogenic (e.g. emitted by factories) • When VOCs combine with NOx in the presence of sunlight (photo-oxidation), SOA is created: H2SO4 + 2NaNO2 2HONO + Na2SO4 HONO OH + NO OH + VOC  products (i.e. SOA, ozone, oVOC, etc.) ISOPOOH, a hydroxyl-hydroperoxide is hypothesized to contribute to SOA formation As VOCs are oxidized, they have lower vapor pressures and become less volatile, and less volatile species are more likely to form aerosols Some isomers of ISOPOOH are linked to the formation of IEPOX, an epoxydiol that has been foundin aerosol samples[3], butisomer-specific experiments are lacking The Keutsch group has recently synthesized two specific isomers of ISOPOOH to investigate the kinetics and yields of IEPOX formation Research Goals Develop a method to inject known amounts of a VOC into the chamber Develop a method to oxidize the VOC Study the oxidation kinetics of ISOPOOH University of Wisconsin—Madison, Chemistry Department Keutsch Group Hannah Grossberg, Jennifer B. Kaiser & Professor Frank Keutsch Atmospheric Simulation Chamber for the Measurement of Volatile Organic Compound Oxidation References and Acknowledgements Oxidized by HONO Oxidize by H2O2, added via bubbler hν ISOPOOH Isoprene IEPOX OR