Frank M. Bowman

Formation of Organic Aerosols from the Oxidation of Biogenic Hydrocarbons

AbstractMeasurements of aerosol formation during thephotooxidation of α-pinene, β-pinene,d-3-carene, d-limonene, ocimene, linalool, terpinene-4-ol, andtrans-caryophyllene were conducted in anoutdoor smog chamber. Daylight experiments in thepresence of

Ozone productivity of atmospheric organics

{\text{NO}}_x

Atmospheric chemistry of alternate fuels and reformulated gasoline components

and dark experiments withelevated ozone concentrations were performed. Theevolution of the aerosol was simulated by theapplication of a gas/particle absorption model inconnection with a chemical reaction mechanism. Thefractional aerosol yield is shown to be a function ofthe organic aerosol mass concentration andtemperature. Ozone and, for selected hydrocarbons, theNO3 reaction of the compounds were found torepresent efficient routes to the formation ofcondensable products. For initial hydrocarbon mixingratios of about 100 ppb, the fractional aerosol yieldsfrom daylight runs have been estimated to be ∼5%for open-chain hydrocarbons, such as ocimene andlinalool, 5–25% for monounsaturated cyclicmonoterpenes, such as α-pinene, d-3-carene, orterpinene-4-ol, and ∼40% for a cyclic monoterpenewith two double bonds like d-limonene. For the onlysesquiterpene investigated, trans-caryophyllene, afractional aerosol yield of close to 100% wasobserved. The majority of the compounds studied showedan even higher aerosol yield during dark experimentsin the presence of ozone.

Fundamental basis of incremental reactivities of organics in ozone formation in VOC/NOx mixtures

Abstract A dynamic model is developed for gas-particle absorptive partitioning of semi-volatile organic aerosols. The model is applied to simulate a pair of m-xylene/NOx outdoor smog chamber experiments. In the presence of an inorganic seed aerosol a threshold for aerosol formation is predicted. An examination of characteristic times suggests conditions where an assumption of instantaneous gas-particle equilibrium is justified. Semi-volatile products that are second-generation, rather than first-generation, products of a parent hydrocarbon cause a delay in aerosol formation due to the delayed rate at which the second-generation products are formed. The gas-particle accommodation coefficient is the principal transport parameter and is estimated to have a value between 1.0 and 0.1 for the m-xylene aerosol.

Gas/Particle Partitioning and Secondary Organic Aerosol Yields

A technique is developed to determine the amount of ozone and other products, such as nitric acid and peroxyacetylnitrate (PAN), generated by the individual organic components of a complex atmospheric organic/NOx mixture. The technique is applied to the SAPRC 90 photochemical mechanism to study the individual contributions of carbonyls, aromatics, alkanes, alkenes, and carbon monoxide to ozone, nitric acid, PAN, and free radical production at varying organic to NOx ratios typical of atmospheric conditions.

Estimated effects of temperature on secondary organic aerosol concentrations.

A technique developed to determine the amount of ozone and secondary photochemical species generated by the individual organic components of a complex atmospheric organic/NOx mixture (Bowman and Seinfeld, J. geophys. Res. 99, 5309–5324 (1994a)) is used to study the individual contributions of carbonyl, aromatic, alkane, and alkene emissions to ozone and secondary organic and inorganic aerosol species in the South Coast Air Basin of California for the Southern California Air Quality Study (SCAQS) air pollution episode of 27–28 August 1987. Aldehydes exhibit the highest ozone productivity followed by alkenes, and lumped reactive aromatics. The aromatic species and formaldehyde enhance the production of secondary organic and secondary sulfate aerosol, because they are effectively OH sources. The same species, through their effect on both OH and O3 production, are also significant precursors of HNO3, and consequently, of nitrate aerosol. This methodology can be used in conjunction with urban airshed models to investigate alternative emission control scenarios.

Estimated effects of composition on secondary organic aerosol mass concentrations

Abstract Recent air quality regulations have mandated the use of reformulated gasoline and alternate fuels in motor vehicles. Reformulated fuels are intended to reduce both ozone-forming volatile organic compound (VOC) emissions and air toxic emissions from vehicles. A method that allows the determination of the individual contributions of a single VOC to the ozone formation in a complex VOC/NOx mixture is outlined and applied to eight potential reformulated fuel components. In calculations using a current comprehensive atmospheric chemical reaction mechanism a wide variety of organics are shown to be responsible for ozone production. The incremental reactivities of the fuel components, which are defined as the additional amount of ozone formed per amount of organic compound added to a base mixture, include both the direct production of ozone by the oxygenate itself and additional ozone produced by the VOC mixture when the oxygenate is added. The enhancement of ozone production attributable to the organic mixture upon adding the oxygenates is shown to be a result of changes to the organic free radical pool. Most of the fuel oxygenates have relatively low incremental reactivities due to their slow reaction rates and to the formation of relatively unreactive formate and acetate products. The more reactive fuel oxygenates are those containing ethyl groups, which react faster than their counterparts containing only methyl and tert-butyl groups.

Theoretical method for lumping multicomponent secondary organic aerosol mixtures.

Abstract The incremental reactivity of a particular organic species refers to the change in the ozone generated upon addition of a small amount of the organic to a complex organic/NOx, mixture undergoing photooxidation. It is known that the values of the incremental reactivities of organic species depend on the composition of the particular organic/NOx, mixture, the hydrocarbon-to-NOx, ratio, and other environmental conditions. Using a method that enables the assignment of the ozone produced in the photo-oxidation of a complex organic/NOx, mixture to each of the individual organics present, we show how the incremental ozone reactivity of any one organic species results from changes in the ozone generated by each of the organics present. Thus, we demonstrate explicitly the dependence of the incremental reactivity of each organic present on the nature of the organic/NOx, mixture. Calculations are presented using the SAPRC 90 chemical mechanism to explain the origin of the variation of incremental reactivities with initial hydrocarbon-to-NOx ratio.