Inter-community variability in total particle number concentrations in the eastern Los Angeles air basin

Abstract

Abstract. Ultrafine Particles (UFP) can display sharp gradients in their number concentrations in urban environment due to their transient nature and rapid atmospheric processing. The ability of using air pollution data generated at a central monitoring station to assess exposure relies on our understanding of the spatial variability of a specific pollutant associated with a region. High spatial variation in the concentrations of air pollutants has been reported at scales of 10s of km for areas affected by primary emissions. Spatial variability in particle number concentrations (PNC) and size distributions needs to be investigated, as the representativeness of a monitoring station in a region is premised on the assumption of homogeneity in both of these metrics. This study was conducted at six sites, one in downtown Los Angeles and five located about 40-115 km downwind in the receptor areas of Los Angeles air basin. PNC and size distribution were measured using Condensation Particle Counters (CPC) and Scanning Mobility Particle Sizer (SMPS). The seasonal and diurnal variations of PNC implied that PNC might vary significantly with meteorological conditions, even though the general patterns at the sites may remain generally similar across the year due to consistency of sources around them. Regionally transported particulate matter (PM) from upwind urban areas of Los Angeles lowered spatial variation by acting as a "homogenizing" factor during favorable meteorological conditions. Spatial variability also increased during hours of the day during which the effects of local sources predominate. The spatial variability associated with PNC (quantified using Coefficients of Divergence, CODs), averaged about 0.3, which was generally lower than that based on specific size ranges. Results showed an inverse relationship of COD with particles size, with fairly uniform values in the particle rangeCorrespondence to: C. Sioutas (sioutas@usc.edu) which is associated with regional transport. Our results suggest that spatial variability, even in the receptor regions of Los Angeles Basin, should be assessed for both PNC and size distributions, and should be interpreted in context of seasonal and diurnal influences, and suitably factored if values for exposure are ascertained using a central monitoring station.

New particle formation at ground level and in the vertical column over the Barcelona area

“…The main source of UFP in urban areas is road traffic (Charron and Harrison, 2003;Pey et al, 2009;Dall'Osto et al, 2013;Kumar et al, 2014;Brines et al, 2014a), and especially diesel engines (Morawska et al, 1998;Harris and Maricq, 2001;Rose et al, 2006;Rodríguez et al, 2007). Thus, studies carried out worldwide show that UFP levels are higher close to major road traffic urban arteries compared with those recorded at urban background sites (Zhu et al, 2002;Wehner et al, 2002;Kittelson et al, 2004;Hudda et al, 2010;Padró-Martínez et al, 2012;Fujitani et al, 2012). The spatial distribution of UFP across the urban environment has been studied in detail in a few cities in Europe , 2013von BismarckOsten et al, 2013;Salma et al, 2014;Brines et al, 2014a) finding that UFP concentrations markedly increased at road sites with respect to the urban background.…”

“…Subsequent studies evidenced the relevance of these episodes in cities from high insolation regions such as southern Europe, California or Australia Costabile et al, 2010;Reche et al, 2011;Hudda et al, 2010;Cheung et al, 2011Cheung et al, , 2015Brines et al, 2014b). This influence is so important that, on an annual average, maximum hourly UFP concentrations at the urban background of Barcelona (Northeast of Spain) are recorded at midday simultaneously with the lowest black carbon (BC) concentrations (Reche et al, 2011).…”

Monitoring PM10 and Ultrafine Particles in Urban Environments Using Mobile Measurements

“…Therefore, the highest concentrations of ultrafine particles are found in the vicinity of the primary sources, for example, near busy roads where particle number concentrations are typically between 10 4 and 10 6 particles/cm 3 depending on driving speed, fleet composition and meteorology (Nikolova et al, 2011) and ultrafine particle number concentrations decrease rapidly with distance from the emission sources (Zhu et al, 2002;Hagler et al, 2010). Therefore important differences, in space and time, of UFP concentrations between urban micro-environments are induced (More et al, 2009;Hudda et al, 2010).…”

Influence of medium range transport of particles from nucleation burst on particle number concentration within the urban airshed

“…In previous studies, particle mass concentration has been studied with regard to long range transport in an intercontinental scale (Jaffe et al, 2003), however the size distribution of and temporal-spatial variations in PNC have only been investigated on a local scale (Morawska et al, 1998;Hussein et al, 2004). For example, although regional nucleation has been observed in Helsinki, Finland (Hussein et al, 2008), Atlanta and Pittsburgh, United States of America 4952 H. C. Cheung et al: Influence of medium range transport (Stolzenburg et al, 2005;Stanier et al, 2004), spatial variations in PNC have also been studied in urban areas in Australia (Mejía et al, 2008) and in the United States (Hudda et al, 2010). These studies have not examined the impact of regional pollution on PNCs or the influence upwind urban pollution has on PNC downwind during the nucleation events.…”