The session consisted of two talks, one by Jeremy Hales outlining NARSTO activities, and a second by Stephen Schwartz focusing on a newly proposed DOE initiative, the Tropospheric Aerosol Program (TAP).

A possible focus of future PM/Ozone research might be the synergisms between ozone concentrations and source terms for other related species. In this context, the possibility of using reactivity as a regulatory tool was suggested. The question was raised: 'How can reactivity be regulated?' NARSTO has started to archive fine particle data with the goal that these data be used to address scientific issues including health effects, visibility, radiative forcing, heterogeneous chemistry, and others. Although feedback is required from the health effects community, finding epidemiologists who can provide useful input has proven difficult. It was mentioned that there is an opportunity for future research activities to use NARSTO as an "umbrella" organization for data archival.

The primary focus of the new Tropospheric Aerosol Program is to define, observe, quantify, and accurately model the processes that control the physical and chemical properties of ambient particles. The radiative forcing and health impacts of ambient particulate matter (PM) are determined mainly by particle size, the size-dependent chemical composition of PM, and the processes that alter size-dependent PM properties. The concentration and chemical composition of ambient PM often vary significantly with particle size, geographical location, and time. Therefore, TAP will focus on elucidating the processes that control the life cycle of ambient PM as a function of geographical location and time. Currently, the plan is for TAP to be focused in four major areas: (1) annual field campaigns that characterize the regional PM and processes controlling regional PM properties over a few hundred kilometer scale, (2) laboratory and theoretical studies in support of field activities, (3) modeling activities to incorporate new results from laboratory and field studies to better characterize PM and processes controlling PM properties within models, and (4) development of new and advanced instrumentation required to observe the life cycle of ambient PM.

Unlike most past programs, the focus in TAP will be on the processes controlling the life cycle of ambient PM. The results from the various TAP activities will help reduce uncertainties in estimates of the direct and indirect effects of PM on climate by going beyond quantifying what is there - to quantifying the mechanisms responsible for the observed particle properties and producing prognostic models to predict future scenarios. Important areas of future research that have been identified include: nucleation, gas-to-particle conversion, chemical reactions, characterization of size-dependent particle chemical composition, cloud droplet activation, and hygroscopic growth. TAP field campaigns will integrate multiple platforms on a regional scale, including ground stations, aircraft, ships, and satellite platforms. TAP activities can complement the intensive, urban center measurements supported under the EPA Supersites program by providing a larger spatial context a greatly improved understanding of the boundary layer processes that impact the observations made by Supersite investigators. A workshop is planned for June 1-4 at BNL to produce a preliminary project plan for submittal to DOE for FY 2001 funding cycle. Lasting approximately ten years, TAP activities will require funding at the 20 to 30 million dollar level each year.