Richard M. Kamens

The use of polycyclic aromatic hydrocarbons as source signatures in receptor modeling

Abstract The purpose of this study was to explore the use of polycyclic aromatic hydrocarbons (PAH) as organic tracers and to demonstrate how their atmospheric chemical reactivity can be incorporated into a chemical mass balance (CMB) model. PAH signatures were characterized for three combustion sources; residential wood combustion, gasoline spark ignition emissions and diesel engine emissions. The ability to source-differentiate using PAH signatures was tested with a numerical simulation program. Signatures with nine different PAH ranging from benzanthracene to coronene and two smaller groups with four PAH were used. Normalized PAH signatures gave better results than un-normalized signatures. It was possible to distinguish between three sources when a minor source contributed more than 10% of the total. The resulting CMB model was evaluated with ambient data from three different studies for which PAH data existed, and receptor modeling had been undertaken using other tracers. Very reasonable results were obtained. PAH reactivity can strongly influence predicted source contributions under warm daytime conditions.

Influence of humidity, sunlight, and temperature on the daytime decay of polyaromatic hydrocarbons on atmospheric soot particles

In this paper we have attempted to quantify the loss of polyaromatic hydrocarbons (PAH) on atmospheric soot particles with respect to the effects of humidity, solar radiation, and temperature. Dilute residential wood smoke and internal gasoline combustion emissions were individually aged in the presence of natural sunlight in 25-m/sup 3/ outdoor Teflon film chambers. Soot particles were collected on filters and analyzed for PAH. In each experiment first-order rate constants were computed for the disappearance of individual PAH. Rate expressions as a function of humidity, light, and temperature were then generated for nine different PAH from the wood smoke experiments. Estimates suggest that, at moderate humidities and temperatures. PAH half-lives in the chamber atmosphere were of the order of 1 h. At very low angle sunlight, very low water vapor concentrations, or very low temperatures. PAH daytime half-lives on airborne soot particles increased for many compounds to a period of days.

Newly characterized products and composition of secondary aerosols from the reaction of α-pinene with ozone

Secondary aerosols from the reaction of α-pinene with ozone were generated in a 190 m3 outdoor Teflon chamber, and products of these aerosols were characterized. Products were separated by gas chromatography and detected with electron-impact mass spectrometry, chemical-impact mass spectrometry, and Fourier transform infrared spectrometry. Because products from the reaction of α-pinene with ozone contain oxidized functional groups such as carboxylic acids and carbonyls, these products are poorly resolved by standard gas chromatography. To use standard chromatographic techniques, derivatization of oxidized functional groups was necessary. Carbonyl products were derivatized with O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydrochloride and carboxylic acids with pentafluorobenzyl bromide. The major identified products were nor-pinonic acid, pinonic acid, 2,2-dimethylcyclobutane-1,3-dicarboxylic acid, pinic acid, and pinonaldehyde. Dicarboxylic acids have lower vapor pressures than either their corresponding di-aldehydes or mono-acids, and have only recently been identified in α-pinene–ozone aerosols. Given their comparatively low vapor pressures, diacids contribute significantly to the aerosol formation process from the reaction of α-pinene with ozone. The composition of these secondary aerosols is strongly influenced by temperature. During the summer experiments, the aerosol composition is dominated by diacids. During the cooler winter experiments, the di-carbonyl and carbonyl-acid products also contributed to the aerosol composition.

A study of characterize indoor particles in three non-smoking homes

Aerosol concentrations and particle size distributions in three middle income homes were characterized over a three day period. Occupants of the homes were non-smokers. A single central sampling location between the kitchen and dining room areas was used in each of the homes. Thirty-seven and 47 mm prototype personal sampling inlets were collocated with two fixed PM10 dichotomous ambient samplers to determine the average concentration of particulate mass during daytime and evening-early morning sampling periods. Particulate concentrations in the three homes ranged from 14 to 42 μg m−3. On average, 37% of the particle mass was collected in a fine (2.5 μm aerodynamic diameter or below) fraction, 26% was observed in a coarse fraction between 2.5 and 10 μm, and 37% was found in a fraction greater than 10 μm. Particle concentrations obtained with prototype personal samplers compared reasonably well to those obtained with 10 μm ambient air dichotomous samplers. Aerosol size information obtained from automated aerosol instruments suggests that the most significant event for generating small particles in all of the households was cooking. Household vacuum sweeping was the most significant large particle generating event. Electron photomicrographs indicated that particles below 1 μm dominate the particle size-number distribution. Biological and mineral based particles predominantly make up the 2.5–10 μm size range.

Some observations on times to equilibrium for semivolatile polycyclic aromatic hydrocarbons

The relative time scales at which semivolatile gas and particle PAH approach equilibrium under both moderate and cool temperatures were investigated. Combustion particles were added directly from a diesel car and a wood stove to a 190 m^3 outdoor Teflon film chamber. The rate of migration of a gas-phase semivolatile PAH to combustion particles at a warm outdoor temperature was explored by volatilizing solid deuterated pyrene (d10-py) in a hot injector (200 °C) into the rural background air in the chamber atmosphere. After 2 h, diesel exhaust was added to the chamber. Results show an initial rapid migration of d10-py from the gas to the particle phase in an attempt to re-establish equilibrium. The relative closeness to equilibrium was monitored by calculating the equilibrium constant Kp overtime as measured by PAH_(part)/(PAH_(gas) x TSP). As gas-phase PAH concentrations changed in the chamber, due to wall losses, particle off-gassing occurred so that Kp was reasonably constant over time. Under cool outdoor conditions (-1 to -4 °C), PAH loss from the particle phase could not keep up with gas-phase PAH wall losses, and the system departed from equilibrium. Kinetic simulations suggested that tens of hours would be required to reestablish 90% of equilibrium concentrations for compounds like phenanthrene and pyrene once they had departed from equilibrium in the particle phase by 34 and 18%, respectively.

Gas and Particle Products Distribution from the Reaction of β-Caryophyllene with Ozone

Gas and particulate reaction products from the ozonolysis of β -caryophyllene (I) in the presence of atmospheric air were investigated using a combination of gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC). A Scanning Mobility Particle Sizer system (3936, TSI) and a Condensation Particle Counter (3025A, TSI) were used to study secondary organic aerosol formation. The nighttime oxidation was carried out in a large outdoor smog chamber (190 m3). A wide range of ring retaining and ring opening products in the gas and particle phase are reported over the course of the reaction. On average, measured gas and particle phase products accounted for ∼64% of the reacted β -caryophyllene (I) carbon. Measurements show that a number of reaction products with low vapor pressure (e.g., β-caryophyllone aldehyde (IV), β-norcaryophyllone aldehyde (V), β-caryophyllonic acid (VIII), β-14-hydroxycaryophyllonic acid (XIV)) were found in the sample taken during the first 20 min of the reaction and may play an important role in the early formation of secondary organic aerosol. A detailed mechanism is proposed to account for most products observed in this investigation.

Mass balance of gaseous and particulate products analysis from α-pinene/NOx/air in the presence of natural sunlight

The daytime oxidation of α-pinene in the presence of natural sunlight and oxides of nitrogen, NOx, was studied in a large outdoor smog chamber using gas chromatograph mass spectrometry as method of identification and quantification. A Scanning Mobility Particle Sizer system (3936, TSA) and a Condensation Particle Counter (3025A, TSA) were used to study the secondary organic aerosol formation, and a filter pack/denuder sampling system was used for simultaneously collecting gas phase and particle phase products for analysis. A gas chromatograph coupled to an electron impact mass spectrometry (GC-EIMS) method is described for the identification and quantification of gas and aerosol products. The sensitivity of the method was sufficient to produce good quality mass spectra over the range of concentrations used in this study, and compares very well with classical methods based on derivatization and liquid chromatography-ion trap mass spectroscopy methods. Mass balances for gaseous and aerosol reaction products are reported over the course of the reaction. More than 16 products were identified and quantified in this study. On average, measured gas and particle phase products accounted for ∼54% to ∼71% of the carbon reacted α-pinene. Measurements show that 10-hydroxypinonic acid, 10-hydroxypinonaldehyde, 4-oxopinonic acid, and 10-oxopinonic acid are observed in the early stage in the aerosol phase and may play an important role in the early formation of secondary aerosols.

Polynuclear aromatic hydrocarbon degradation by heterogeneous reactions with N2O5 on atmospheric particles

Abstract The degradation of particulate polynuclear aromatic hydrocarbons (PAH) on atmospheric soot particles in the presence of gas phase dinitrogen pentoxide (N2O5) was explored. Dilute diesel and wood soot particles containing PAH were reacted with∼10ppm of N2O5 in a 200 l continuous stirred tank reactor (CSTR). To provide a stable source of particles for reaction in the CSTR, diesel or wood soot particles were injected at night into a 25 m3 Teflon outdoor chamber. The large chamber served as a reservoir for the feed aerosol, and the aerosol could then be introduced at a constant flow rate into the CSTR. PAH-N2O5 heterogeneous rate constants for wood soot at 15°C ranged from2 × 10−18to5 × 10−18 cm3 molecules−1 s−1. For diesel soot the rate constants at 16°C were higher and ranged from5 × 10−18to30 × 10−18 cm3 molecules−1 s−1. Comparisons with other studies suggest that sunlight is the most important factor which influences PAH decay. This is followed by ozone, NO2, N2O5 and nitric acid. The rate constants of nitro-PAH formation from a parent PAH and N2O5 were of the order of1 × 10−19−1 × 10−18 molecules−1s−1. The uncertainty associated with all of these rate constants is± a factor of 3. Given, however, the small magnitude of the rate constants and the low levels of N2O5 present in the atmosphere, we concluded that PAH heterogeneous reactions with gas phase N2O5 degrade particle-bound PAH or to form nitro-PAH from PAH arenot very important. (Direct application of the specific rate constants derived in this study to ambient atmospheres should not be undertaken unless the ambient particle size distributions and chemical composition of the particles are similar to the ones reported in this study.)

Organosulfates as Tracers for Secondary Organic Aerosol (SOA) Formation from 2-Methyl-3-Buten-2-ol (MBO) in the Atmosphere

2-Methyl-3-buten-2-ol (MBO) is an important biogenic volatile organic compound (BVOC) emitted by pine trees and a potential precursor of atmospheric secondary organic aerosol (SOA) in forested regions. In the present study, hydroxyl radical (OH)-initiated oxidation of MBO was examined in smog chambers under varied initial nitric oxide (NO) and aerosol acidity levels. Results indicate measurable SOA from MBO under low-NO conditions. Moreover, increasing aerosol acidity was found to enhance MBO SOA. Chemical characterization of laboratory-generated MBO SOA reveals that an organosulfate species (C5H12O6S, MW 200) formed and was substantially enhanced with elevated aerosol acidity. Ambient fine aerosol (PM2.5) samples collected from the BEARPEX campaign during 2007 and 2009, as well as from the BEACHON-RoMBAS campaign during 2011, were also analyzed. The MBO-derived organosulfate characterized from laboratory-generated aerosol was observed in PM2.5 collected from these campaigns, demonstrating that it is a molecular tracer for MBO-initiated SOA in the atmosphere. Furthermore, mass concentrations of the MBO-derived organosulfate are well correlated with MBO mixing ratio, temperature, and acidity in the field campaigns. Importantly, this compound accounted for an average of 0.25% and as high as 1% of the total organic aerosol mass during BEARPEX 2009. An epoxide intermediate generated under low-NO conditions is tentatively proposed to produce MBO SOA.

Effect of composition and state of organic components on polycyclic aromatic hydrocarbon decay in atmospheric aerosols.

published in Advance ACS Abstracts, September 15, 1994. Envlron. Scl. Technol., Vol. 28, No. 12, 1994 2153