Abstract. Fuel treatments in fire-suppressed mixed-conifer forests are designed to moderate potential wildfire behavior and effects. However, the objectives for modifying potential fire effects can vary widely, from improving fire suppression efforts and protecting infrastructure, to reintroducing low-severity fire, to restoring and maintaining variable forest structure and wildlife habitat. In designing a fuel treatment, managers can alter the treatment's prescription, placement, and extent (collectively the "treatment strategy") to optimally meet one objective. However, the potential for trade-offs among different objectives is rarely tested systematically in fire-prone landscapes. To evaluate trade-offs in mechanical fuel treatment objectives related to fire severity, smoke production, forest heterogeneity, and avian wildlife habitat, we used a cross-platform modeling approach based on spatially explicit modifications of forest structure data for a 7820-ha landscape in the Lake Tahoe Basin, California. We examine whether (1) a more uniform treatment strategy aimed at fire hazard reduction (FHR) had negative effects on wildlife diversity, (2) a strategy focused on protecting the wildland-urban interface (WUI) left other portions of the landscape vulnerable to high-severity fire, and (3) increasing the extent of fuel treatments across the landscape led to greater reductions in fire severity and smoke emissions. When approximately 13% of the landscape was treated, the proportion of the landscape vulnerable to high-severity fire decreased by 13-44%, with the more uniform FHR strategy leading to greater reductions. Slight increases in predicted avian species richness that followed all treatment strategies were not closely linked to increases in canopy variability. The WUI protection strategy led to considerable reductions in fire severity at the landscape scale. Increasing the extent of treatments to 30% of the landscape did little to further reduce the area vulnerable to high-severity fire, with additional reductions of 4-7% depending on the prescription. However, increasing the extent of treatments reduced the extent of harmful downwind smoke impacts, primarily by reducing rate of fire spread. Treatment strategies will depend on specific management objectives, but we illustrate that trade-offs are not necessarily inherent in general outcomes of fuel treatments.
On-road particle size distributions were measured at the Tuscarora Mountain tunnel on the Pennsylvania Turnpike in May 1999. The data were obtained using a scanning mobility particle sizer. The nucleation modes of the size distributions contained most of the particles on a number concentration basis and exhibited peak diameters ranging from 11 to 17 nm. This observation is consistent with previous calculations and measurements, indicating that signi cant numbers of ultra ne aerosol particles can be expected in close proximity to busy motorways. The experiment provided 4 case studies for which the tunnel inlet data could be used to correct data obtained at the outlet, allowing for estimates of particle production within the tunnel. Exhaust particle production rates per vehicle kilometer were estimated; the results are presented with the caveat that the measurements were affected by ambient dilution. The 4 case study nucleation mode sizes varied inversely with ambient temperature. The light-duty vehicle contributions to the ultra ne particle distributions were apparently dominated by the heavy-duty vehicle contributions.
Recent studies have linked atmospheric fine particulate matter (PM 2.5 ) with human health effects. In many urban areas, mobile sources are the dominant source of PM 2.5 . Dynamometer studies have also implicated diesel engines as being a significant source of ultrafine particles. In order to characterise particulate emissions from in-use vehicles, we performed an onroad study of emissions from vehicles operating in the Tuscarora Mountain Tunnel along the Pennsylvania Turnpike. As part of this study we obtained chemically speciated, size-segregated PM emission rates, particle size distributions, chemically speciated profiles of diesel emissions for use in source apportionment studies, a comparison with years past how much improvement there has actually been in diesel particulate emission rates, and measurements of particulate emission rates from light-duty gasoline vehicles to evaluate the relative significance of this source. This paper describes the experimental methods and presents the preliminary results of the on-road particulate emissions measurements.
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