Diesel soot aging in urban plumes within hours under cold dark and humid conditions.

Fresh and aged diesel soot particles have different impacts on climate and human health. While fresh diesel soot particles are highly aspherical and non-hygroscopic, aged particles are spherical and hygroscopic. Aging and its effect on water uptake also controls the dispersion of diesel soot in the atmosphere. Understanding the timescales on which diesel soot ages in the atmosphere is thus important, yet knowledge thereof is lacking. We show that under cold, dark and humid conditions the atmospheric transformation from fresh to aged soot occurs on a timescale of less than five hours. Under dry conditions in the laboratory, diesel soot transformation is much less efficient. While photochemistry drives soot aging, our data show it is not always a limiting factor. Field observations together with aerosol process model simulations show that the rapid ambient diesel soot aging in urban plumes is caused by coupled ammonium nitrate formation and water uptake.

Revisiting the commons: local lessons, global challenges.

In a seminal paper, Garrett Hardin argued in 1968 that users of a commons are caught in an inevitable process that leads to the destruction of the resources on which they depend. This article discusses new insights about such problems and the conditions most likely to favor sustainable uses of common-pool resources. Some of the most difficult challenges concern the management of large-scale resources that depend on international cooperation, such as fresh water in international basins or large marine ecosystems. Institutional diversity may be as important as biological diversity for our long-term survival.

Elderly in the traffic environment: analysis of fatal crashes in northern Sweden.

Fatal crashes of the elderly (> or = 60 years; N = 379) in northern Sweden in the traffic environment, between 1977 and 1986, were investigated using autopsy and police reports. Males had double the death rate of females. The car occupants made up the largest category (43%) followed by pedestrians, pedalcyclists, and two-wheel-motorvehicle (TWMV) riders, but the risk of fatal injury per unit distance travelled was highest for pedestrians and pedalcyclists. Most car occupants were killed in vehicle-vehicle crashes, mostly in the daylight and at intersections or straight roads. Ice and/or snow (31%) was the major precrash factor. In two-thirds of single car crashes, roadside hazards such as trees were involved. Most elderly fatally injured car drivers were responsible for the crash, and they were commonly involved in collisions with oncoming vehicles. Only 4% of the fatally injured car drivers were driving under the influence of alcohol. Head injuries appeared to be more common in side impact than in frontal impacts. Serious chest injuries were more common than head injuries in car crashes. One-quarter of the pedestrians were injured at pedestrian crossings and about half during darkness. One in six pedestrians were under the influence of alcohol. All pedalcyclists were injured in collisions with motor vehicles and most were injured at intersections. Pedestrians, pedalcyclists, and TWMV riders had more serious head injuries than chest injuries.

Head and face injuries in bicyclists--with special reference to possible effects of helmet use.

Fatal and nonfatal head and face injuries to unhelmeted bicyclists were analyzed to assess the injury-reducing potential of bicycle helmet use. Of the fatally injured, 64% (median age, 55 years) had fatal head and face injuries compared with 38% (median age, 18 years) with head and face injuries in the nonfatal injury group. The fatally injured often had multiple impact points, mostly to the occipital and temporal regions. Brain contusions, most often to the frontal and temporal lobes, were the most common cause of fatal injury, followed by subdural hematomas. In the nonfatal injury group abrasions/lacerations were most common type of injury, followed by cerebral concussions/contusions and superficial contusions. If all types of injuries to bicyclists are taken into account a helmet might have had an injury-reducing effect in two of every five fatal cases and in one of every five nonfatal cases. To increase the helmet use among bicyclists, a law, as in Australia, would be an excellent instrument.