Intra-Community Variability in Total Particle Number Concentrations in the San Pedro Harbor Area (Los Angeles, California)

Author： Moore Katharine

Publisher： Taylor & Francis Ltd

ISSN： 1521-7388

Source： Aerosol Science and Technology, Vol.43, Iss.6, 2009-06, pp. : 587-603

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Abstract

Recent evidence links elevated ultrafine particle (UFP) concentrations with adverse health effects, but exposure assessments based upon PM2.5 mass concentrations may be misleading. In order to better understand and quantify intra-community variability in UFP concentrations, a dense network of 14 monitoring sites was set-up in Los Angeles in two clusters—San Pedro/Wilmington and West Long Beach—in communities surrounding the Ports of Los Angeles and Long Beach. The network measured total particle number concentrations greater than 7 nm in diameter. In this range, UFP comprise approximately 90% of the total. Port-related activities—particularly goods movement associated with high volumes of heavy-duty diesel vehicle (HDDV) traffic—represent significant UFP sources. The field study was conducted from mid-February through mid-December 2007 to assess diurnal, seasonal, and spatial patterns and intra-community variability in total particle number concentrations. For sites within a few km of each other, simultaneous particle number concentrations can vary up to a factor of 10 (< 10,000="" cm-3="" up="" to="" 90,000="" cm-3="" for="" hourly="" averages="" calculated="" by="" month).="" the="" median="" hourly="" correlation="" coefficient="" (r)="" across="" all="" sites="" was="" modest="" and="" varied="" from="" 0.3="" to="" 0.56.="" specific="" site="" locations,="" particularly="" proximity="" to="" roadways="" used="" for="" goods="" movement,="" strongly="" affect="" observations.="" clear="" diurnal="" and="" seasonal="" patterns="" are="" evident="" in="" the="" data.="" a="" diurnal="" pattern="" associated="" with="" high="" hddv="" volumes="" and="" goods="" movement="" was="" identified.="" coefficients="" of="" divergence="" calculated="" for="" the="" site="" pairs="" suggest="" moderate="" heterogeneity="" overall="" (median="" study="" cod="" ≍="" 0.35).="" the="" intra-urban="" variability="" observed="" in="" this="" study="" is="" comparable="" to="" and="" exceeds="" the="" inter-urban="" variability="" observed="" in="" a="" previous="" study="" in="" los="" angeles.="" ufp="" concentrations="" can="" vary="" considerably="" on="" short="" spatial="" scales="" in="" source-rich="" environments="" strongly="" influencing="" the="" accuracy="" of="" exposure="" assessments.="">