Ultrafine particle (UFP) number concentrations vary significantly on smallspatial and temporal scales due to their short atmospheric lifetimes andmultiplicity of sources. To determine UFP exposure gradients within acommunity, simultaneous particle number concentration measurements at anetwork of sites are necessary. Concurrent particle number size distributionmeasurements aid in identifying UFP sources, while providing data toinvestigate local scale effects of both photochemical and physical processeson UFP. From April to December 2007, we monitored particle number sizedistributions at 13 sites within 350 m–11 km of each other in the vicinityof the Ports of Los Angeles and Long Beach using Scanning Mobility ParticleSizers (SMPS). Typically, three SMPS units were simultaneously deployed androtated among sites at 1–2 week intervals. Total particle numberconcentration measurements were conducted continuously at all sites.Seasonal and diurnal number size distribution patterns are complex, highlydependent on local meteorology, nearby PM sources, and times of day, andcannot be generalized over the study area nor inferred from one or twosampling locations. Spatial variation in particle number size distributionswas assessed by calculating the coefficient of divergence (COD) andcorrelation coefficients () between site pairs. Results show an overallinverse relationship between particle size and CODs, implying that numberconcentrations of smaller particles (40 nm) differ from site to site,whereas larger particles tend to have similar concentrations at varioussampling locations. In addition, variations in r values as a function ofparticle size are not necessarily consistent with corresponding COD values,indicating that using results from correlation analysis alone may notaccurately assess spatial variability.
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