Norman F. Robinson

The IMPROVE_A Temperature Protocol for Thermal/Optical Carbon Analysis: Maintaining Consistency with a Long-Term Database

Abstract Thermally derived carbon fractions including organic carbon (OC) and elemental carbon (EC) have been reported for the U.S. Interagency Monitoring of PROtected Visual Environments (IMPROVE) network since 1987 and have been found useful in source apportionment studies and to evaluate quartz-fiber filter adsorption of organic vapors. The IMPROVE_A temperature protocol defines temperature plateaus for thermally derived carbon fractions of 140 °C for OC1, 280 °C for OC2, 480 °C for OC3, and 580 °C for OC4 in a helium (He) carrier gas and 580 °C for EC1, 740 °C for EC2, and 840 °C for EC3 in a 98% He/2% oxygen (O2) carrier gas. These temperatures differ from those used previously because new hardware used for the IMPROVE thermal/optical reflectance (IMPROVE_TOR) protocol better represents the sample temperature than did the old hardware. A newly developed temperature calibration method demonstrates that these temperatures better represent sample temperatures in the older units used to quantify IMPROVE carbon fractions from 1987 through 2004. Only the thermal fractions are affected by changes in temperature. The OC and EC by TOR are insensitive to the change in temperature protocol, and therefore the long-term consistency of the IMPROVE database is conserved. A method to detect small quantities of O2 in the pure He carrier gas shows that O2 levels above 100 ppmv also affect the comparability of thermal carbon fractions but have little effect on the IMPROVE_TOR split between OC and EC.

Real-world automotive emissions : Summary of studies in the Fort McHenry and Tuscarora Mountain Tunnels

Al~ract--Motor vehicle emission rates of CO, NO, NOx, and gas-phase speciated nonmethane hydrocarbons (NMHC) and carbonyl compounds were measured in 1992 in the Fort McHenry Tunnel under Baltimore Harbor and in the Tuscarora Mountain Tunnel of the Pennsylvania Turnpike, for comparison with emission-model predictions and for calculation of the reactivity of vehicle emissions with respect to 03 formation. Both tunnels represent a high-speed setting at relatively steady speed. The cars at both sites tended to be newer than elsewhere (median age was < 4 yr), and much better maintained as judged by low CO/CO2 ratios and other emissions characteristics. The Tuscarora Mountain Tunnel is flat, making it advantageous for testing automotive emission models, while in the underwater Fort McHenry Tunnel the impact of roadway grade can be evaluated. MOBILE4.1 and MOBILE5 gave predictions within + 50% of observation most of the time. Tbere was a tendency to overpredict, especially with MOBILE5 and especially at Tuscarora. However, fight-dutyvehicle CO, NMHC, and NOx all were underpredicted by MOBILE4.1 at Fort McHenry. Light-dutyvehicle CO/NO~ ratios and NMHC/NO~ ratios were generally a little higher than predicted. The comparability of the predictions to the observations contrasts with a 1987 experiment in an urban tunnel (Van Nuys) where CO and HC, as well as CO/NO~ and NMHC/NO~ ratios, were grossly underpredicted. The effect of roadway grade on gram per mile (g mi- 1) emissions was substantial. Fuel-specific emissions (g gal-1), however, were almost independent of roadway grade, which suggests a potential virtue in emissions models based on fuel-specific emissions rather than g mi- 1 emissions. Some 200 NMHC and carbonyl emissions species were quantified as to their light- and heavy-dutyvehicle emission rates. The heavy-duty-vehicle NMHC emissions were calculated to possess more reactivity, per vehicle-mile, with respect to 03 formation (g 03 per vehicle-mile) than did the light-duty-vehicle NMHC emissions. Per gallon of fuel consumed, the light-duty vehicles had the greater reactivity. Much of the NMHC, and much of their reactivity with respect to O3 formation, resided in compounds heavier than Cto, mostly from beavy-duty diesels, implying that atmospheric NMHC sampling with canisters alone is inadequate in at least some situations since canisters were found not to be quantitative beyond ~ C1o. The contrasting lack of compounds heavier than C1o from light-duty vehicles suggests a way to separate light- and heavy-duty-vehicle contributions in receptor modeling source apportionment. The division between light-duty-vehicle tailpipe and nontaiipipe NMHC emissions was ~ 85% tailpipe and ~ 15% nontailpipe (evaporative running losses, etc.). Measured CO/CO2 ratios agreed well with concurrent roadside infrared remote sensing measurements on light-duty vehicles, although remote sensing HC/CO2 ratio measurements were not successful at the low HC levels prevailing. Remote sensing measurements on heavy-duty diesels were obtained for the first time, and were roughly in agreement with the regular (bag sampling) tunnel measurements in both CO/CO2 and HC/CO2 ratios. A number of recommendations for further experiments, measurement methodology development, and emissions model development and evaluation are offered. Copyright

The USEPA/DRI chemical mass balance receptor model, CMB 7.0

Abstract This paper presents the U.S. Environmental Protection Agencys Chemical Mass Balance Model developed in cooperation with the Desert Research Institute, Reno, NV. CMB 7.0 apportions source contributions to pollutants measured at a receptor site, using measured profiles of the source chemical and elemental compositions. The model incorporates uncertainties in both the pollutant measurements and the source profile measurements in producing contribution estimates and their standard errors.

Performance of the chemical mass balance model with simulated local-scale aerosols

Abstract A general methodology for performing simulations of the Chemical Mass Balance (CMB) model is developed and applied to simple and complex local scale scenarios. The simple scenario consists of crustal, coal-fired power plant, motor vehicle and vegetative burning sources; the complex scenario adds oil-fired power plant, ocean, steel mill, lead smelter, municipal incinerator and background aerosol sources. Daily receptor filter concentrations of the most commonly measured elements in the primary emissions are simulated. These simulations incorporate daily fluctuations in source strengths, daily fluctuations in source profiles (as parameterized by a coefficient of variation, or CV, of temporal source profiles) and measurement error at the receptor (as parameterized by a CV of measurement error). The CMB is applied to each daily measurement using a source library containing all sources and their long-term profiles (which, though correct on average, are incorrect on any particular day). The extent of agreement of the actual and CMBestimated primary emission source strengths is measured as an average absolute error (AAE, the absolute difference between the daily actual and estimated primary emission source strengths averaged over 100 simulated days). These moderately realistic simulations provide an encouraging picture of CMB accuracy and precision. The CMB yields acceptable accuracy and precision (an AAE of 50% or less) even when the CV of temporal source profiles is 25% and the CV of measurement error is 10%.

Comparison of MOBILE4.1 and MOBILE5 predictions with measurements of vehicle emission factors in Fort McHenry and Tuscarora mountain tunnels

Abstract Measurements of motor vehicle emissions at Tuscarora Tunnel in Pennsylvania and Fort McHenry Tunnel in Maryland were compared with predictions of the U.S. Environmental Protection Agency (USEPA) mobile-source emission models MOBILE4.1 and MOBILE5. Both models usually agreed to within ± 50% with the observed emission rates, with MOBILES consistently predicting higher emission factors than MOBILE4.1. At Tuscarora, which is level, both models tended to overpredict. At Fort McHenry, which has grades, MOBILE4.1 underpredicted, and MOBILE5 overpredicted.

Comparison of Particle Light Scattering and Fine Particulate Matter Mass in Central California

Abstract Particle light scattering (Bsp) from nephelometers and fine particulate matter (PM2.5) mass determined by filter samplers are compared for summer and winter at 35 locations in and around California’s San Joaquin Valley from December 2, 1999 to February 3, 2001. The relationship is described using particle mass scattering efficiency (σsp) derived from linear regression of Bsp on PM2.5 that can be applied to estimated PM2.5 from nephelometer data within the 24-hr filter sampling periods and between the every-6th-day sampling frequency. An average of σsp =4.9 m2/g was found for all of the sites and seasons; however, σsp averaged by site type and season provided better PM2.5 estimates. On average, the σsp was lower in summer than winter, consistent with lower relative humidities, lower fractions of hygroscopic ammonium nitrate, and higher contributions from fugitive dust. Winter average σsp were similar at non-source-dominated sites, ranging from 4.8 m2/g to 5.9 m2/g. The σsp was 2.3 m2/g at the roadside, 3.7 m2/g at a dairy farm, and 4.1 m2/g in the Kern County oilfields. Comparison of Bsp from nephelometers with and without a PM2.5 inlet at the Fresno Super-site showed that coarse particles contributed minor amounts to light scattering. This was confirmed by poorer correlations between Bsp and coarse particulate matter measured during a fall sampling period.

The importance of liquid water concentration in the atmospheric oxidation of SO2

The concentration of condensed water available for aqueous chemical reactions is viewed as a fundamental parameter of the heterogeneous conversion of gaseous SO2 to particulate sulfate. New results from a series of dispersed-phase experiments in a cloud chamber, in which the magnitude of this parameter was allowed to vary widely, demonstrate that the heterogeneous SO2 conversion rate in hazes is generally limited by the small concentration of condensed water. This limitation precludes the heterogeneous oxidation pathway from being important in the atmosphere during haze episodes except under extreme conditions of high humidities and aerosol loadings. In clouds, on the other hand, the liquid water concentrations are relatively large, permitting chemically related factors, such as pH-dependent equilibria and oxidant abundances, to limit the SO2 conversion rate.

MOBILE4.1/5 reweighting software

Abstract This paper presents software developed by the Desert Research Institute to read MOBILE4.1/5 output and reweight the emission factors with user-given travel fractions. Composite emission factors are calculated for comparison with experimental tunnel measurements. This software can be used to model any fixed segment of roadway with known traffic composition.

Technical Note: On the Calibration of an Opticle Particle Counter

Mie scattering theory is used to calculate the relative optical responses for latex and water particles in the diameter range 0.3 to 15 μm, using geometry applicable to a Royco 225 Optical Particle Counter. The results are presented in a way that permits direct correction of the instrumental calibration curve for the refractive index differences associated with the calibration and sample aerosol particles

A fast numerical procedure for determining the saddle point of a free energy surface

Abstract A fast numerical procedure is presented for locating free energy of formation surface saddle points for sulfuric acid and water or other binary systems.