Leland Tarnay

Exhaust Particle Size Distribution Measurements at the Tuscarora Mountain Tunnel

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 significant numbers of ultrafine 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 ultrafine particle distributions were apparently dominated by the heavy-duty vehicle contributions.

Preliminary measurements of summer nitric acid and ammonia concentrations in the Lake Tahoe Basin air-shed: implications for dry deposition of atmospheric nitrogen

Over the past 50 years, Lake Tahoe, an alpine lake located in the Sierra Nevada mountains on the border between California and Nevada, has seen a decline in water clarity. With significant urbanization within its borders and major urban areas 130 km upwind of the prevailing synoptic airflow, it is believed the Lake Tahoe Basin is receiving substantial nitrogen (N) input via atmospheric deposition during summer and fall. We present preliminary inferential flux estimates to both lake surface and forest canopy based on empirical measurements of ambient nitric acid (HNO3), ammonia (NH3), and ammonium nitrate (NH4NO3) concentrations, in an effort to identify the major contributors to and ranges of atmospheric dry N deposition to the Lake Tahoe Basin. Total flux from dry deposition ranges from 1.2 to 8.6 kg N ha-1 for the summer and fall dry season and is significantly higher than wet deposition, which ranges from 1.7 to 2.9 kg N ha-1 year-1. These preliminary results suggest that dry deposition of HNO3 is the major source of atmospheric N deposition for the Lake Tahoe Basin, and that overall N deposition is similar in magnitude to deposition reported for sites exposed to moderate N pollution in the southern California mountains.

Estimating contribution of wildland fires to ambient ozone levels in National Parks in the Sierra Nevada, California

Data from four continuous ozone and weather monitoring sites operated by the National Park Service in Sierra Nevada, California, are used to develop an ozone forecasting model and to estimate the contribution of wildland fires on ambient ozone levels. The analyses of weather and ozone data pointed to the transport of ozone precursors from the Central Valley as an important source of pollution in these National Parks. Comparisons of forecasted and observed values demonstrated that accurate forecasts of next-day hourly ozone levels may be achieved by using a time series model with historic averages, expected local weather and modeled PM values as explanatory variables. Results on fire smoke influence indicated occurrence of significant increases in average ozone levels with increasing fire activity. The overall effect on diurnal ozone values, however, was small when compared with the amount of variability attributed to sources other than fire.

Chapter 24 A Statistical Model for Forecasting Hourly Ozone Levels During Fire Season

Concerns about smoke from large high-intensity and managed low intensity fires have been increasing during the past decade. Because smoke from large high-intensity fires are known to contain and generate secondary fine particles (PM2.5) and ozone precursors, the effect of fires on air quality in the southern Sierra Nevada is a serious management issue. Various process-based models have been developed for forecasting PM and ozone levels in the presence and absence of fires. Although these models provide deterministic predictions, few of them give measures of uncertainties associated with these predictions. Estimates of uncertainties are essential for model evaluation and forecasting with known precision levels. In this chapter we present a statistical procedure for forecasting next-day ozone levels at given sites. The statistical model takes into account some of the known sources of ozone fluctuations, including changes in temperature, humidity, wind speed, wind direction and, during fire season, effects of smoke from fires. Other sources of variation not directly accounted for in the model—e.g., variability in daily amount of ozone produced by sources other than fire—are included in the uncertainty measure as random effect variables. The advantage of a model that is capable of estimating mean effects and uncertainties simultaneously is that evaluation of model performance is immediate and predictions are available with specific precision levels. The ability of the model in making accurate forecasting with specified precisions is demonstrated by applying it to real data set of observed ambient ozone and weather values at two sites in the Sierra Nevada for the period from 1 January to 31 July 2006. Forecasted PM2.5 values from the BlueSky Smoke Dispersion Model are tested as a proxy for the amount of pollution precursors reaching a given site from specific fires. The forecasts from the statistical model may be useful as a tool for air quality managers to time-prescribed fire treatment.

A Modeling Study to Estimate the Sources of Atmospheric Nitrogen Deposition in the Lake Tahoe Basin

Lake Tahoe, which is located between the California-Nevada borders, is famous for its clarity; however, decline in Lake Tahoe’s water clarity was reported as 0.25 m per year1. Nutrient loading (phosphorus and nitrogen (N)) in last decades has been shown as the primary cause for this decline, and nearly half of total N input to the lake was attributed to atmospheric deposition.