The technical tasks to be accomplished in Phase 1 are in order of priority:
Scrubber design. The initial and primary focus will be the collection of particulates, but the scrubbing of the gases arising from internal combustion –- NO, CO2, SO2 –- will also be considered. Desired operating conditions will be determined, such as anticipated airflow (desired vehicle speed range), particulate concentrations, and a detailed description of weather conditions and ranges. A trade study will be conducted to engage vendors and designers for each potential scrubbing modality: HEPA filter, wet scrubbing, electrostatic precipitation. An industrial HEPA filter will be examined first as the solution anticipated to have the least cost and complexity.
Characterization of particulate distributions. We reviewed measurements of on - and near - road particulate concentrations, as well as simulations of near-road pollutant dispersal in the presence of roadside barriers, many of them EPA-funded research. We intend to make this review comprehensive. We also conducted preliminary transient modeling of particulate distributions in Ansys Fluent using 6- lane expressway geometry, 3- meter- high roadside barriers, and a 5 m/sec cross wind. The source term was derived from on-road measurements of semi truck particulate emissions. Particulate pollution was modelled as n-octane vapor. Results indicate that, using a scrubbing period of 5 minutes, no more than 10% of particulates escaped the roadway. This model will be further developed to include varying barrier heights, traffic conditions, temperatures, and wind speeds –- all with an eye toward developing an algorithm for determining scrubbing frequencies in real time.
Vehicle design. A concept scrubbing vehicle will be designed. The objectives will be to maximize the airflow (vehicle cross section), package the scrubbing equipment, and account for the consequent aerodynamic forces. A rough cost to manufacture the vehicle and the annual cost to operate and maintain the vehicle will be determined.
Program design. A sample program will be developed for a large metropolitan area. Routes will be determined based on traffic volume, particularly diesel trucks, and hours of daily congestion.
To demonstrate the cost effectiveness of this concept, we developed a simple preliminary program for Chicago, using a scrubbing period of 5 minutes., Chicago has approximately 100 miles of regularly congested expressway through areas of high population density. A rough calculations of costs:
Given a scrubbing period of 5 minutes, if the scrubbing vehicle travels on the shoulder of these roads at an average speed of 20 mph, 60 vehicles are required.
Approximately 120 mile range required per vehicle for a 6 hour congestion period.
Another 40 vehicles may be required for off-peak hours / night operations, and reserve capacity, for a total fleet number of approximately 100 vehicles.
Rough costs: $1 million per vehicle; driver salaries and benefits (pre-autonomy), $100,000 per year; vehicle maintenance and pollutant handling/disposal, $100,000 per year.
Total annual cost to the city over 10 years is $30 million per year. This doesn’t include the cost of additional barriers. Many of these routes currently have sound barriers.
The benefits of this technology are reduction of disease due to air pollution, primarily fine particulates,; and mitigation of climate change due to reduction of black carbon particles. A 2005 study for the British Columbia Lung Association showed that a 1% reduction of ambient PM2.5 would produce $29 million in annual savings in the Metro Vancouver region. Assuming a 90% reduction of particulates on major expressways and arterials, and exposure weighted by population density and commuters, a metro area could see (conservatively) a 50% reduction in total particulate exposure. If the cost per year is $30 million, this equates to a (very rough) cost-benefit ratio of 1:50.
A major source of black carbon is diesel exhaust. Black carbon is responsible for up to 40% of net observed global warming. Because black carbon remains in the atmosphere for only a few weeks, reducing black carbon emissions may be the fastest means of slowing climate change in the near term, and consequently avoiding an approaching tipping point. A significant impact thereon can be expected by the removal of the bulk of mobile-source black carbon in urban areas.
As these benefits accrue to society at large, the customer for this technology will be primarily government entities. A vehicle fleet of 100 to 200 vehicles for a large metropolitan area is financially feasible. The intensive, top- down approach reflected in a relatively small fleet of dedicated vehicles is suitable for places where individual compliance with vehicle emissions standards is lax.