The physicochemical properties of summertime ambient ultrafine particles in southwest Detroit: Sources and atmospheric processes (Michigan)

Ambient ultrafine particles (UFPs; diameters <0.1 mum) are receiving increasing attention for their potential toxicity and roles in visibility and climate. The primary objective of this study is to resolve the dominant sources and atmospheric processes influencing the number-size distribution of UFPs. Measurements of trace-element size distribution in fine particles (<2.5 mum), gas pollutants, and meteorological parameters were also made concurrently at an urban Detroit site over 42 days in the summers of 2003--2005.; A systematic approach was developed for identification and classification of UFP events, defined as periods with prolonged and elevated UFP number concentration. Case studies of the UFP events suggest the majority of the events were related to traffic and industrial plumes. Strong evidence is presented for atmospheric nucleation (new particle formation) in polluted urban areas during daylight hours, indicating the nucleation is photochemically-driven. These events do not directly result from fossil-fuel combustion and are distinguished by the gradual increase of particle surface area due to the ensuing particle growth. The relatively low surface area preceded the events suggests conditions in which heterogeneous condensation is less favored.; The source and meteorological influences on size-resolved UFPs were examined using factor analysis and time series techniques on a highly time and size resolved aerosol/gas/meteorology data set, which included a 5-min resolution and 107 particle size fractions. The results indicate the major UFP sources are gasoline-powered vehicles, diesel-powered vehicles, and atmospheric nucleation/SO 2 plumes, in a sequence of decreasing contributions to larger particles. Meteorological conditions associated with the three UFP sources are low wind speeds, daylight hours, and solar radiation, respectively. Furthermore, PM 2.5 and SO2 are strongly associated with local industrial plumes. An analysis of wind direction and time dependence of the factors confirms known source locations and follows the diurnal pattern of traffic in Detroit.; The analysis presented here identified the major source and meteorological influences on the pollutants impacting the site, including size-resolved UFPs, PM2.5, and ozone. The significance of these factors was quantified at a high-temporal resolution which has important applications to real-world exposure studies examining the role of copollutants and meteorology on health endpoints.