Peter J. Groblicki

Problems in the sampling and analysis of carbon particulate

Abstract Several thermal and wet chemical methods of separating organic from elemental carbon in particulate samples were examined. It is concluded that none of them represents an ideal separation procedure and that only a method-dependent operational definition of organic and elemental carbon is possible at this time. The best separation method appears to be a thermal procedure using 350°C air oxidation followed by pyrolysis in He at 950°C. There are also difficulties in sampling since dual filter techniques show that adsorption of organic compounds on various filter media accounted for at least 15 per cent of the total organic carbon collected during ambient sampling in Warren, MI. This adsorption further confuses the results and needs to be studied at other sampling sites.

Real-World Emissions from a Modern Production Vehicle Driven in Los Angeles

The emissions of hydrocarbons, nitric oxide, and carbon monoxide from one modern vehicle were measured using on-board instrumentation during about 350 miles of driving in Los Angeles, California. Emissions during on-road driving were compared to those obtained on dynamometers using the urban dynamometer driving schedule (UDDS). Although this study only used one driver and vehicle, tested over a relatively short distance, the analysis technique may be useful for a larger evaluation of off-cycle emissions. The test vehicle had low warmed-up running emissions over the UDDS and for most of the on-road testing where the air-to-fuel ratio was maintained at the stoichiometric point. However, occasional heavily-loaded conditions during the on-road testing led to richerthan-stoiehiometric operation. During these brief enrichment events, which lasted up to 29 seconds, CO emissions were increased by a factor of 2500 and HC by a factor of 40 over closed-loop stoichiometric operation. Nitrogen oxide emissions were sim...

Chemical analysis of size-segregated samples of Denver's ambient particulate

Size-segregated impactor samples of Denvers wintertime airborne particulate were analyzed for the major chemical species. These species are responsible for most of the pollution-related visibility reduction in Denver. Samples were collected three times a day during a 40-day field program in November-December, 1978. Each of the measured chemical species (sulfate, nitrate, ammonium, bromide, organic and elemental carbon) had a log-normally distributed accumulation mode with a mass median aerodynamic diameter near 0.3 ..mu..m. For all species, particle size increased with increasing relative humidity. These results are supported by electrical aerosol analyzer (EAA) measurements. The impactor results for this time period are consistent with a photochemical mechanism for particulate nitrate formation and a heterogeneous mechanism for the formation of sulfate particles. 23 references, 5 figures, 5 tables.

Particulate Carbon at Various Locations in the United States

Particulate elemental and organic carbon concentrations were determined on filters collected between 1972 and 1980 at ten United States’ sites representing urban, suburban, rural, and remote areas. The results showed that particulate elemental carbon is ubiquitous with mean concentrations ranging from 1.1 micrograms per cubic meter at the remote site in South Dakota to 13.3 micrograms per cubic meter in a congested area in New York City. About 80% of the elemental carbon mass consists of particles with a diameter of less than 2.5 micrometers. Particulates in this size range are responsible for most pollutant-related visibility reductions. Since it appears that elemental carbon is the only light-absorbing particulate species, the specific light-absorption coefficient for elemental carbon was calculated to be 12.7 m2/g while the specific light-scattering coefficient was 3.2 m2/g. Using these coefficients, the contributions of elemental carbon to the observed visibility reduction at the various sites are estimated. These range from 6 to 38%. Also discussed are the seasonal and diurnal variations of particulate elemental and organic carbon as well as the contribution from secondary organic particulates. In addition, an updated carbon-source apportionment, based on recent analytical developments, is presented for the Denver area.

Measurement of the removal rate of elemental carbon from the atmosphere

Measurements of the removal rate of elemental carbon from the atmosphere were performed for 7 weeks in Seattle and for 5 months at 12 rural sites in Sweden. Rainwater samples were collected in glass jars, while a similar container protected from rainfall was used to estimate the contribution of dry deposition to the rainwater samples. Wet deposition accounted for most of the flux of elemental carbon to the glass collection vessels, with a median wet deposition flux of 4 mg m−2 mo−1 in both Seattle and Sweden. The wet deposition flux of elemental carbon in Sweden showed a weak north-south gradient. Median concentrations of elemental carbon in rainwater were 60 and 100 μgL−1 in Seattle and Sweden, respectively, with the highest concentrations associated with the lowest rainfall amounts.

Denver's visibility history

Abstract The National Weather Services historical visibility record for Denver is found not to apply to downtown Denver, but to the surrounding metropolitan area. The meteorology and topography are largely responsible for the discrepancy between the prevailing visibilities recorded by the National Weather Service and air quality measured within the city. Historically, the visibility for metropolitan Denver declined 10–20% over the 1948–1978 period. The summer quarter consistently experienced the worst visibility and the greatest decline over the period. In the fall and winter quarters when the ‘brown cloud’ occurs most prominently, trends in the 60th and 90th percentile visibility do not show a persistent deterioration.