Spatial and Temporal Characterization of PM_2.5 Mass Concentrations in California, 1980–2007

Abstract

Systematic measurement of fine particulate matter (aerodynamic diameter less than 2.5 m [PM 2.5 ]) mass concentrations began nationally with implementation of the Federal Reference Method (FRM) network in 1998 and 1999. In California, additional monitoring of fine particulate matter (PM) occurred via a dichotomous sampler network and several special studies carried out between 1982 and 2002. The authors evaluate the comparability of FRM and non-FRM measurements of PM 2.5 mass concentrations and establish conversion factors to standardize fine mass measurements from different methods to FRMequivalent concentrations. The authors also identify measurements of PM 2.5 mass concentrations that do not agree with FRM or other independent PM 2.5 mass measurements. The authors show that PM 2.5 mass can be reconstructed to a high degree of accuracy (r 2 Ͼ 0.9; mean absolute error ϳ2 g m Ϫ3 ) from PM with an aerodynamic diameter Յ10 m (PM 10 ) mass and species concentrations when site-specific and season-specific conversion factors are used and a statewide record of fine PM mass concentrations by combining the FRM PM 2.5 measurements, non-FRM PM 2.5 measurements, and reconstructions of PM 2.5 mass concentrations. Trends and spatial variations are evaluated using the integrated data. The rates of change of annual fine PM mass were negative (downward trends) at all 22 urban and 6 nonurban (Interagency Monitoring of Protected Visual Environments [IMPROVE]) monitoring locations having at least 15 yr of data during the period 1980 -2007. The trends at the IMPROVE sites ranged from Ϫ0.05 to Ϫ0.25 g m Ϫ3 yr Ϫ1 (median Ϫ0.11 g m Ϫ3 yr Ϫ1 ), whereas urban-site trends ranged from Ϫ0.13 to Ϫ1.29 g m Ϫ3 yr Ϫ1 (median Ϫ0.59 g m Ϫ3 yr Ϫ1 ). The urban concentrations declined by a factor of 2 over the period of record, and these decreases were qualitatively consistent with changes in emissions of primary PM 2.5 and gas-phase precursors of secondary PM. Mean PM 2.5 mass concentrations ranged from 3.3 to 7.4 g m Ϫ3at IMPROVE sites and from 9.3 to 37.1 g m Ϫ3 at urban sites.

Historical Prediction Modeling Approach for Estimating Long-Term Concentrations of PM2.5in Cohort Studies before the 1999 Implementation of Widespread Monitoring

“…Another possible reason for this poor performance is that the CARB dichot network used a different sampling protocol from that used by FRM. Our simplified data-driven calibration method may not have performed well when compared with an approach incorporating site-specific meteorological conditions (Blanchard et al 2011). Model performance may have also been affected by a set of CARB dichot sites in the highest PM 2.5 concentration areas (Figure 4).…”

“…For model evaluation in years prior to 1999, we obtained PM 2.5 data from three different networks in addition to IMPROVE: the Southern California Children’s Health Study (CHS) for 1988–2001 (Peters et al 2004), the California Air Resources Board dichotomous sampler monitoring (CARB dichot) for 1994–2003 in California (Blanchard et al 2011), and the Inhalable Particulate Network (IPN) for 1979–1982 over the continental United States (Hinton et al 1985). CHS PM 2.5 data collected using 2-week samplers were converted to FRM-equivalent PM 2.5 data for computing annual averages (Peters et al 2004).…”

“…CHS PM 2.5 data collected using 2-week samplers were converted to FRM-equivalent PM 2.5 data for computing annual averages (Peters et al 2004). Likewise, for the CARB dichot data, we adopted a published conversion equation to estimate FRM-equivalent PM 2.5 (Blanchard et al 2011). We applied the same inclusion criteria to sites in the three model evaluation networks to compute annual averages.…”

Spatial and Temporal Variability of the PM2.5/PM10 Ratio in Wuhan, Central China

“…PM 2.5 was not systematically observed and reported in United States until 1998, and it has just been introduced into the air quality monitoring system in 2013 in China (Yu and Wang, 2010). Identifying and quantifying the PM 2.5 /PM 10 ratios can provide useful information for retrospective prediction of PM 2.5 concentration without direct PM 2.5 measurements, which has been successfully applied in California and Taipei (Yu and Wang, 2010;Blanchard et al, 2011;Chu et al, 2015). However, all of these applications of the PM 2.5 /PM 10 ratio need evidence of its spatio-temporal variability.…”

A Severe Air Pollution Event from Field Burning of Agricultural Residues in Beijing, China

“…Integrated near-ground air pollutant monitoring and satellite remote sensing allow to effectively analyze spatial and temporal variations in PM 2.5 concentrations during severe air pollution events, as has been reported by numerous researchers (Liu et al, 2009;Blanchard et al, 2011;Chudnovsky et al, 2013;Nordio et al, 2013;Pope and Wu, 2014). The spatial distributions of different emission sources may generate different spatial and temporal variation patterns for pollutants.…”