.|  Baltimore Ecosystem Study
Meteorological Research Projects

Monitoring and modeling solar radiation in urban environments
  • Gordon M. Heisler, USDA Forest Service
  • Richard H. Grant, Purdue University
  • Alan Berkowitz, Cary Institute of Ecosystem Studies
UV radiation impacts urban environments in numerous ways. Potential effects on human health include skin cancers, cataracts of the eye, and immune deficiencies. UV radiation also affects health of plants and animals in both terrestrial and aquatic ecosystems, the potency of pests and pathogens, biogeochemical cycles, plant community composition, and air quality

Monitoring of the solar UV irradiance at the Earth's surface is routinely carried out at about 70 locations in the United States. The majority of these sites are located in rural locations to assess UV impacts on agriculture and rural ecosystems and to determine long-term irradiance trends. However, most of the population lives in metropolitan areas where scattering by primary and secondary atmospheric pollutants make it difficult to extrapolate above-canopy and below-canopy UV irradiance from rural UV-irradiance measurements. Greater scattering by pollutants in the urban boundary layer may enhance the penetration of UV radiation to the ground level in the shade of trees and buildings.

BES is planning for a solar radiation-monitoring site, to include UV radiation, for the city of Baltimore. The monitoring station will be located on the flat roof of a water surge tower at the Ashburton Water Filtration Plant in the city of Baltimore and near the center of the Gwynns Falls Watershed. The sky view from this site is essentially unobstructed in all directions. Initially, the radiation monitoring station will be equipped with a broadband UVB pyranometer measuring Ultraviolet-B (UVB, 280-320 nm) radiation, a sensor to measure the photosynthetically active radiation (PAR, 400 to 700 nm), and a pyranometer to measure global solar radiation (300-3000 nm). A goal of the project is to disseminate the measured values via the World Wide Web. Near real-time data access is important for educational purposes (discussed below), and will greatly facilitate data quality control and station management.

Figure 1. Ozone (trangles) and UV radiation monitoring stations relative to the 1999 maximum ozone concentrations in Baltimore / Washington, DC Area. Isopleths of maximum ozone concentrations range from 115 ppb to greater than 155 ppb with a 5 ppb interval. Triangles denote ozone monitors, circles denote UV monitors.

For analysis of the BES solar measurements, supporting meteorological measurements are made at the BES reference meteorology station (19 km away), at a partial National Weather Service (NWS) ASOS (Automated Surface Observing System) station at the Maryland Science Center (6 km away), and a complete ASOS station at Baltimore Washington Airport (BWI, 16 km away). Supporting radiation measurements are made in the Baltimore area: at a station in Sterling VA as part of the Integrated Surface Irradiance Study (ISIS) network of the National Oceanic and Atmospheric Administration (NOAA), and at the Maryland Science Center as part of the Aeronet network of National Aeronautics and Space Administration. Global short wave (SW, 300-3000 nm), incoming and reflected PAR, and all-wave net radiation are also measured at the BES reference meteorology station. Global, sky, and solar beam SW radiation are measured at the ISIS station. Solar beam and sky radiation at 440, 670, 870, and 1020 nm are measured at the Maryland Science Center.

Supporting UV radiation measurements are made at a variety of locations including the Smithsonian Research Institution (Edgewater, MD) and at USDA locations at more rural Beltsville and Queenstown, MD. Air quality monitoring of surface PM10, NO2, SO2, and O3, along with wind speed and wind direction are made at a number of locations in the Baltimore area as part of the EPA state air quality monitoring (Fig. 1).

An important component of the National Science Foundation mandate for urban LTER's is that research results be shared with the community and that researchers work with the community in the application of results. The need for public education on UV radiation hazards is well recognized in the United States and other countries, including by NOAA and EPA, which sponsor the UV Index in the USA. A goal for the BES UV monitoring station is to enhance the utility of the UV Index locally by providing real-time values of UVB irradiance so that educators can point out irradiance in relation to time of day and current sky conditions.

There are several possible applications of the monitored radiation data in research. Models of tree and building effects on solar irradiance including the UVB require validation measurements of relative irradiance below tree canopies and in building shade. The Ashburton monitoring site will provide above-canopy irradiance for normalizing below-canopy irradiance measurements similar to the methods used by Grant and Heisler in previous research. Another research need is determination of the relationship of UV radiation in urban areas to tropospheric air pollutants UV actinic and radiant fluxes will be modeled at scales ranging from local neighborhoods to the Baltimore-Washington metropolitan area. Studies will include evaluation of the interactions between the UV radiation and atmospheric pollutants. The 'rural' USDA UV-B Monitoring Network site to the east of Baltimore at Queenstown provides the ability to make urban/rural comparisons under certain weather patterns and provides measures of the column ozone and aerosol optical thickness. The Ashburton monitoring site will also support other BES research. A variety of studies are examining ecosystem relationships in BES. For example, one study is investigating the factors that contribute to the invasiveness of exotic species. Changes in relative intensity of UV irradiance, particularly the UV to PAR ratio may influence the competitive ability of species in a plant community.

The national LTER office is reviewing a request prepared by Heisler, Berkowitz, and Grant (BES) and Brazel and Day (CAPLTER) for travel funds for planning comparative UV monitoring, research, and education in BES and CAPLTER in Phoenix. This planning would include representatives of the USDA UVB Radiation Monitoring Program, University of Maryland, and the Smithsonian.

Additional information on UV studies is included in (Grant et al. 2000),Grant, R.H., G.M. Heisler, and J.R. Slusser. 2000. Urban UV measurements: Rationale for the establishment of long-term monitoring in the Baltimore Ecsystem Study. In: Third Urban Environment Symposium. Davis, CA. 14-18 August 2000. American Meteorological Society. Boston, MA. pp. 195-196.