Wavelength-dependent intersystem crossing dynamics of phenolic carbonyls in wildfire emissions.

Quantum chemical calculations were employed to construct Jablonski diagrams for a series of phenolic carbonyls, including vanillin, iso-vanillin, 4-hydroxybenzaldehyde, syringaldehyde, and coniferyl aldehyde. These molecules can enter the Earth's atmosphere from forest fire emissions and participate in photochemical reactions within the atmospheric condensed phase, including cloud and fog droplets and aqueous aerosol particles. This photochemistry alters the composition of light-absorbing organic content, or brown carbon, in droplets and particles through the formation and destruction of key chromophores.

Changes in Chemical Composition and Copepod Toxicity during Petroleum Photo-oxidation.

Photoproducts can be formed rapidly in the initial phase of a marine oil spill. However, their toxicity is not well understood. In this study, oil was irradiated, chemically characterized, and tested for toxicity in three copepod species (, , and ).

Highly Resolved Composition during Diesel Evaporation with Modeled Ozone and Secondary Aerosol Formation: Insights into Pollutant Formation from Evaporative Intermediate Volatility Organic Compound Sources.

As stricter regulations continue to reduce vehicular emissions, other emission sources such as evaporative emissions from road building and volatile consumer products have become more important in overall pollutant forming emissions in many urban areas. Emission regulations have historically targeted volatile organic compounds (VOCs) to reduce ozone, but intermediate volatility organic compounds (IVOCs) also contribute to ozone formation and the formation of secondary organic aerosol (SOA) that often dominates fine particulate matter. Emission rates and pollutant formation from IVOCs are not well constrained in current inventories and models.

Detailed Speciation of Intermediate Volatility and Semivolatile Organic Compound Emissions from Gasoline Vehicles: Effects of Cold-Starts and Implications for Secondary Organic Aerosol Formation.

Over the past two decades vehicle emission standards in the United States have been dramatically tightened with the goal of reducing urban air pollution. Secondary organic aerosol (SOA) is the dominant contributor to urban organic aerosol. Experiments were conducted at the California Air Resources Board Haagen-Smit Laboratory to characterize exhaust organics from 20 gasoline vehicles recruited from the California in-use fleet.

Unimolecular Decay of the Dimethyl-Substituted Criegee Intermediate in Alkene Ozonolysis: Decay Time Scales and the Importance of Tunneling.

We used the steady-state master equation to model unimolecular decay of the Criegee intermediate formed from ozonolysis of 2,3-dimethyl-2-butene (tetramethylethylene, TME). Our results show the relative importance and time scales for both the prompt and thermal unimolecular decay of the dimethyl-substituted Criegee intermediate, (CH)COO. Calculated reactive fluxes show the importance of quantum mechanical tunneling for both prompt and thermal decay to OH radical products.

Reducing secondary organic aerosol formation from gasoline vehicle exhaust.

On-road gasoline vehicles are a major source of secondary organic aerosol (SOA) in urban areas. We investigated SOA formation by oxidizing dilute, ambient-level exhaust concentrations from a fleet of on-road gasoline vehicles in a smog chamber. We measured less SOA formation from newer vehicles meeting more stringent emissions standards.

Comparison of Gasoline Direct-Injection (GDI) and Port Fuel Injection (PFI) Vehicle Emissions: Emission Certification Standards, Cold-Start, Secondary Organic Aerosol Formation Potential, and Potential Climate Impacts.

Recent increases in the Corporate Average Fuel Economy standards have led to widespread adoption of vehicles equipped with gasoline direct-injection (GDI) engines. Changes in engine technologies can alter emissions. To quantify these effects, we measured gas- and particle-phase emissions from 82 light-duty gasoline vehicles recruited from the California in-use fleet tested on a chassis dynamometer using the cold-start unified cycle.

Molecular Characterization of Organosulfur Compounds in Biodiesel and Diesel Fuel Secondary Organic Aerosol.

Secondary organic aerosol (SOA), formed in the photooxidation of diesel fuel, biodiesel fuel, and 20% biodiesel fuel/80% diesel fuel mixture, are prepared under high-NO conditions in the presence and absence of sulfur dioxide (SO), ammonia (NH), and relative humidity (RH). The composition of condensed-phase organic compounds in SOA is measured using several complementary techniques including aerosol mass spectrometry (AMS), high-resolution nanospray desorption electrospray ionization mass spectrometry (nano-DESI/HRMS), and ultrahigh resolution and mass accuracy 21T Fourier transform ion cyclotron resonance mass spectrometry (21T FT-ICR MS). Results demonstrate that sulfuric acid and condensed organosulfur species formed in photooxidation experiments with SO are present in the SOA particles.

Effect of Organic Coatings, Humidity and Aerosol Acidity on Multiphase Chemistry of Isoprene Epoxydiols.

Multiphase chemistry of isomeric isoprene epoxydiols (IEPOX) has been shown to be the dominant source of isoprene-derived secondary organic aerosol (SOA). Recent studies have reported particles composed of ammonium bisulfate (ABS) mixed with model organics exhibit slower rates of IEPOX uptake. In the present study, we investigate the effect of atmospherically relevant organic coatings of α-pinene (AP) SOA on the reactive uptake of trans-β-IEPOX onto ABS particles under different conditions and coating thicknesses.

Organic matrix effects on the formation of light-absorbing compounds from α-dicarbonyls in aqueous salt solution.

Aqueous-phase reactions of organic compounds are of general importance in environmental systems. Reactions of α-dicarbonyl compounds in the aqueous phase of atmospheric aerosols can impact their climate-relevant physical properties including hygroscopicity and absorption of light. Less-reactive water-soluble organic compounds may contribute an organic matrix component to the aqueous environment, potentially impacting the reaction kinetics.

Fuel composition and secondary organic aerosol formation: gas-turbine exhaust and alternative aviation fuels.

A series of smog chamber experiments were performed to investigate the effects of fuel composition on secondary particulate matter (PM) formation from dilute exhaust from a T63 gas-turbine engine. Tests were performed at idle and cruise loads with the engine fueled on conventional military jet fuel (JP-8), Fischer-Tropsch synthetic jet fuel (FT), and a 50/50 blend of the two fuels. Emissions were sampled into a portable smog chamber and exposed to sunlight or artificial UV light to initiate photo-oxidation.

Pressure dependence of stabilized Criegee intermediate formation from a sequence of alkenes.

Ozonolysis is a key reaction in atmospheric chemistry, although important details of the behavior of the ozonolysis intermediates are not known. The key intermediate in ozonolysis, the Criegee intermeiate (CI), is known to quickly isomerize, with the favored unimolecular pathway depending on the relative barriers to isomerization. Stabilized Criegee intermediates (SCI), those with energy below any barriers to isomerization, may result from initial formation with low energy or collisional stabilization of high energy CI.

Adventures in ozoneland: down the rabbit-hole.

In this perspective we describe a 15 year pursuit of the Stabilized Criegee Intermediate (SCI). We have conducted several complementary experiments to measure the pressure dependence of product yields-including OH radical and ozonides-on sequences of alkene + ozone systems. In so doing we have been able to bring into gradual focus a succession of weakly bound intermediates, starting with the primary ozonide, then the SCI, and finally a vinyl hydroperoxide (VHP) product of SCI rearrangement.

2,3-Dimethyl-2-butene (TME) ozonolysis: pressure dependence of stabilized Criegee intermediates and evidence of stabilized vinyl hydroperoxides.

We present measurements of the pressure dependence of stabilized Criegee intermediate (SCI) formation utilizing a hexafluoroacetone scavenger. SCI yields in the ozonolysis of 2,3-dimethyl-2-butene (TME) were measured in a high pressure flow reactor within a range of 50-710 Torr. Within this pressure range, SCI yields increase linearly with pressure.

The HOOH UV spectrum: importance of the transition dipole moment and torsional motion from semiclassical calculations on an ab initio potential energy surface.

The absorption cross section of HOOH, a starting point for larger ROOH, was calculated using the "Wigner method." Calculations use the Wigner transform of ground state wave functions and classical approximations for excited state wave functions. Potential energy and transition dipole moment surfaces were calculated using the equation-of-motion coupled-cluster singles and doubles method over an extended Franck-Condon region.