Airborne particles are implicated in respiratory diseases including asthma. As cities often have elevated particle counts and high asthma rates, designing tree plantings to increase interception is considered to be one way of cleaning air, thereby improving human health. This project studies particle deposition to leaf surfaces under both controlled conditions and in the field in order to 1) improve our understanding of deposition kinetics; 2) develop species specific rate constants for deposition; 3) develop landscape scale metrics of human exposure risk; 4) correlate particle size and concentration with immune response.

Asthma incidence in urban populations has increased in recent years, especially among children in places like the Bronx. Asthma correlates with the concentration of fine particulates in the air and remedies such as tree planting to intercept particles have been proposed to bring states into compliance with federal regulations. Despite the widely held belief that because tree canopies contain large surface area they are effective air filters, there is surprisingly little detailed quantitative information about of trees’ performance in removing particles from the air. There is need for improved estimates of trees’ filtration ability at the scale of species, stand and landscape. Human health concerns everyone; making the right policy decisions is premised on having accurate information on which to base the policy.

We have addressed the problem of trees and their particle filtration ability though a hierarchy of experiments involving wind tunnel studies to quantify the effect of leaf morphology, leaf area and leaf density, field monitoring to determine the contributions of distance from source, and presence/absence of trees on fine particulate distribution. We have also collected particle samples and have used an immunoassay to evaluate their ability to induce proinflammatory cytokines. We have communicated with target audiences via seminars, scientific poster presentations and are planning a high profile symposium for stakeholders to be held in June, 2008.

The major impact thus far is to demonstrate that small scale stochastic particulate "events" occur quite frequently and may play role in inducing acute asthma attacks.These events dominate at the near ground scale where city residents spend most of their outdoor time and are not detected by official monitors. This finding may influence where monitoring stations are located in the future, which in turn could lead to more refined epidemiological relationships between particle concentration and asthma. Mortality and morbidity rates for cardiopulmonary disease are typically expressed in terms of occurrences per 100,000 in the population, so percent decrease in loss of human life will be difficult to establish and in any event, will require retrospective longitudinal studies.

Gretchen Ferenz