Steven M. Japar

Hydroxyl Radical Concentrations Measured in Ambient Air

Diurnal variations in the hydroxyl radical concentration of ambient air were measured for the first time by the technique of laser-induced fluorescence.

The contribution of elemental carbon to the optical properties of rural atmospheric aerosols

Measurements of carbonaceous aerosol, aerosol light absorption and aerosol light scattering were made at two rural sites in southwestern Pennsylvania during August 1983. Aerosol light absorption ranged from 5.2 × 10−6 m−1 to 6.4 × 10−5 m−1 (average: 1.9 × 10−5 m−1) and accounted for about 13% of the aerosol total light extinction. Elemental carbon, averaging 1.3 μg m−3 at the two sites (and comprising some 36 % of the aerosol carbon), accounted for effectively all (> 95 %) of the aerosol light absorption.

Fourier transform infrared kinetic studies of the reaction of HONO with HNO3, NO3 and N2O5 at 295 K

The kinetics of the reaction of nitrous acid (HONO) with nitric acid (HNO3), nitrate radicals (NO3) and dinitrogen pentoxide (N2O5) have been studied using Fourier transform infrared spectroscopy. Experiments were performed at 700 torr total pressure using synthetic air or argon as diluents. From the observed decay of HONO in the presence of HNO3 a rate constant of k<7×10-19 cm3 molecule-1 s-1 was derived for the reaction of HONO with HNO3. From the observed decay of HONO in the presence of mixtures of N2O5 and NO2 we have also derived upper limits for the rate constants of the reactions of HONO with NO3 and N2O5 of 2×10-15 and 7×10-19 cm3 molecule-1 s-1, respectively. These results are discussed with respect to previous studies and to the atmospheric chemistry of HONO.

Fourier transform infrared studies of the reaction of Cl atoms with PAN, PPN, CH3OOH, HCOOH, CH3COCH3 and CH3COC2H5 at 295±2 K

The relative rate technique has been used to measure rate constants for the reaction of chlorine atoms with peroxyacetylnitrate (PAN), peroxypropionylnitrate (PPN), methylhydroperoxide, formic acid, acetone and butanone. Decay rates of these organic species were measured relative to one or more of the following reference compounds; ethene, ethane, chloroethane, chloromethane, and methane. Using rate constants of 9.29×10−11, 5.7×10−11, 8.04×10−12, 4.9×10−13, and 1.0×10−13 cm3 molecule−1 sec−1 for the reaction of Cl atoms with ethene, ethane, chloroethane, chloromethane, and methane respectively, the following rate constants were derived, in units of cm3 molecule−1 s−1: PAN, <7×10−15; PPN, (1.14±0.12)×10−12; HCOOH, (2.00±0.25)×10−13; CH3OOH, (5.70±0.23)×10−11; CH3COCH3, (2.37±0.12)×10−12; and CH3COC2H5, (4.13±0.57)×10−11. Quoted errors represent 2σ and do not include possible systematic errors due to errors in the reference rate constants. Experiments were performed at 295±2 K and 700 torr total pressure of nitrogen or synthetic air. The results are discussed with respect to the previous literature data and to the modelling of nonmethane hydrocarbon oxidation in the atmosphere.In recent discussions with Dr. R. A. Cox of Harwell Laboratory, UKAEA, we learnt of a preliminary value for the rate constant of the reaction of Cl with acetone of (2.5±1.0)×10−12 cm3 molecule−1 sec−1 measured by R. A. Cox, M. E. Jenkin, and G. D. Hayman using molecular modulation techniques. This value is in good agreement with our results.

Comparison of Solvent Extraction and Thermal-Optical Carbon Analysis Methods: Application to Diesel Vehicle Exhaust Aerosol

Filter samples of particulate emissions from two diesel automobiles were analyzed by solvent extraction with a hot toluene/1-propanol mixture, by thermal-optical carbon analysis, and by X-ray fluorescence analysis. On the average, carbon accounted for 83% of the particulate matter, and organic carbon comprised 70% of the extractable mass. The ratio of elemental carbon as measured by the thermal-optical technique to unextractable mass was 1.05 +/- 0.04. For most of the filters the unextractable mass was predominantly elemental carbon. However, for the filters with the largest amounts of unextracted material the elements Fe, S, Al, Si, and Ca were present in significant amounts (0.3-5% each of the unextractable mass when expressed as oxides). 29 references.

Atmospheric acidity measurements on allegheny mountain and the origins of ambient acidity in the Northeastern United States

Abstract Atmospheric acidity as HNO3(g), SO2(g), and aerosol H+ was measured on Allegheny Mountain and Laurel Hill in southwest Pennsylvania in August 1983. The aerosol H+ appeared to represent the net after H2SO4 reaction with NH3(g). The resulting H + SO 4 2− ratio depended on SO42− concentration, approaching that of H2SO4 at the highest SO42− concentrations. The atmosphere was acidic; the average concentrations of HNO3 (78 nmole m−3) and aerosol H+ (205 nmole m−3), NH4+ (172 nmole m−3) and SO42− (201 nmole m−3), and the dearth of NH3(〈 15 nmolem−3), show that the proton acidity (HNO3, H2SO4) of the air exceeded the acid-neutralizing capacity of the air by a factor of > 2, with one 10-h period averaging 263 and 844 nmolem−3 for HNO3 and aerosol H+, respectively. SO2 added another 900 nmole m−3 (average) of potential H+ acidity. HNO3 and aerosol H+ episodes were concurrent, on 7–8 day cycles, unrelated to SO2 which existed more in short-lived bursts of apparently more local origin. NOx was sporadic like SO2. Laurel and Allegheny, separated by 35.5 km, were essentially identical in aerosol SO42−, and in aerosol H+, less so in HNO3 and especially less so in SO2; apparently, chemistry involving HNO3 and aerosol H+ or SO42− was slow compared to inter-site transport times (1–2 h). From growth of bscat and decline of SO2 during one instance of inter-site transport, daytime rate coefficients for SO2 oxidation and SO2 dry deposition were inferred to have been, respectively, ~ 0.05 and ⩽ 0.1 h−1. HNO3 declined at night. Aerosol H+ and SO42− showed no significant diurnal variation, and O3 showed very little; these observations, together with high PAN NO x ratios, indicate that regional transport rather than local chemistry is governing. The O3 concentration (average 56 ppb or 2178 nmolem−3) connotes an oxidizing atmosphere conducive to acid formation. Highest atmospheric acidity was associated with (1) slow westerly winds traversing westward SO2 source areas, (2) local stagnation, or (3) regional transport around to the back side of a high pressure system. Low acidity was associated with fast-moving air masses and with winds from the northerly directions; upwind precipitation also played a moderating role in air parcel acidity. Much of the SO2 and NOx, and ultimately of the HNO3 and aerosol H+, appeared to originate from coal-fired power plants. An automotive contribution to the NOx and HNO3 could not be discerned. Size distributions of aerosol H+ and SO42− were alike, with MMED ~ 0.7 μm, in the optimum range for efficient light scattering and inefficient wet/dry removal. Thus, light scattering and visual range degradation were attributable to the acidic SO42− aerosol, linking the issues of acid deposition and visual air quality in the Northeast. With inefficient removal of aerosol H+, and inefficient night-time removal of HNO3, strong acids may be capable of long-distance transport in the lower troposphere. We obtained an accounting of aerosol mass in terms of composition, including aerosol H2O which was shown to account for much of the light scattering.

Light absorption by airborne aerosols: comparison of integrating plate and spectrophone techniques.

An excellent correlation between the integrating plate (IP) and the photoacoustic methods for measuring aerosol light absorption has been found for airborne graphitic carbon in diesel vehicle exhaust. However, the regression coefficient depends on the orientation of the Teflon membrane filter during the IP analysis. With the collected particulates between the filter and the integrating plate, the IP response is 1.85 times that for the filter reversed. In either case the response ratio of the IP method to the photoacoustic method is >1.0, i.e., 2.43 vs 1.30. The IP calibration is also probably dependent on the nature of the filter medium.

Real-time, in situ measurements of atmospheric optical absorption in the visible via photoacoustic spectroscopy—II. Validation for atmospheric elemental carbon aerosol

Photoacoustic spectroscopy has been applied to real-time measurements of atmospheric elemental carbon (EC) aerosol in ambient air in Dearborn, Michigan. The spectrometer used a photoacoustic cell constructed to operate in the azimuthal mode with acoustic resonant enhancement. The light source was an argon ion laser with the wavelength selected at 514.5 nm. The technique measures optical absorption and was calibrated with NO2 which has a known absorption coefficient. The instrument signal was shown to be quite sensitive to temperature and humidity, so frequent calibration was necessary as the ambient conditions changed. No influence from atmospheric light scattering species was found. Since visible light absorption in the atmosphere is due almost entirely to EC aerosol and NO2 gas, interference from atmospheric NO2 was eliminated by removing it from the sample with a denuder. Optical absorption of the atmospheric aerosol was converted to EC concentration using an absorption coefficient of 10 m2 g−1. Realtime, in situ atmospheric measurements were validated by correlating photoacoustic EC concentrations integrated over several hours with companion filter samples analyzed thermally. Regression of these data gave y = 1.10 (±0.13)x−0.10 (±0.22) with r = 0.926, where y was photoacoustically determined carbon and x was filter carbon in μm−3. The detection limited was 0.3 μgCm−3.

Mutagenicity and chemical characteristics of carbonaceous particulate matter from vehicles on the road.

Experiments were conducted in the Allegheny Mountain Tunnel of the Pennsylvania Turnpike in 1979 to evaluate bacterial mutagenicities of particulate emissions from heavy-duty diesels and gasoline-powered vehicles in highway operation. Filter samples were extracted with dichloromethane followed by acetonitrile. Ames assays with and without microsomal activation, HPLC fluorescence profiles, GC molecular weight distributions, and particle size distributions were obtained. We find that (1) the diesel particulate matter at Allegheny resembles that encountered in dilution-tube studies by all criteria studied (particulate mass emission rate, extractability, particle size, extract HPLC profile, extract molecular weight distribution, and mutagenicity--though these findings do not preclude the possibility of substantial differences in detailed chemical properties), (2) in revertants per microgram of dichloromethane-extracted material at Allegheny, the mutagenicities of the diesel particulate matter and of the local rural ambient particulate matter are of the same order of magnitude, and (3) in revertants per kilometer traveled, the mutagenicity of particulate emissions from heavy-duty diesels is several times (median approx.6 times) that of emissions from gasoline-powered vehicles.

Laser‐induced dissociation of ozone and resonance fluorescence of OH in ambient air

In the measurement of hydroxyl (OH) concentrations in air using the technique of resonance fluorescence, it was established that the presence of ambient ozone led to significant interference. It is concluded that this is a result of OH formation due to laser‐induced dissociation of ozone. A reduction in the power density of excitation was required to reduce this effect to a negligible level.