Spatial Variation of Aerosol Chemical Composition and Organic Components Identified by Positive Matrix Factorization in the Barcelona Region

The spatial distribution of PM₁ components in the Barcelona metropolitan area was investigated using on-road mobile measurements of atmospheric particle- and gas-phase compounds during the DAURE campaign in March 2009. Positive matrix factorization (PMF) applied to organic aerosol (OA) data yielded 5 factors: hydrocarbon-like OA (HOA), cooking OA (COA), biomass burning OA (BBOA), and low volatility and semivolatile oxygenated OA (LV-OOA and SV-OOA). The area under investigation (∼500 km²) was divided into six zones (city center, harbor, industrial area, precoastal depression, 2 mountain ranges) for measurements and data analysis. Mean zonal OA concentrations are 4.9–9.5 μg m^–3. The area is heavily impacted by local primary emissions (HOA 14–38%, COA 10–18%, BBOA 10–12% of OA); concentrations of traffic-related components, especially black carbon, are biased high due to the on-road nature of the measurements. The formation of secondary OA adds more than half of the OA burden outside the city center (SV-OOA 14–40%, LV-OOA 17–42% of OA). A case study of one measurement drive from the shore to the precoastal mountain range furthest downwind of the city center indicates the importance of nonfossil over anthropogenic secondary OA based on OA/CO

Trends in Chemical Composition of Global and Regional Population-Weighted Fine Particulate Matter Estimated for 25 Years

We interpret in situ and satellite observations with a chemical transport model (GEOS-Chem, downscaled to 0.1° × 0.1°) to understand global trends in population-weighted mean chemical composition of fine particulate matter (PM_2.5). Trends in observed and simulated population-weighted mean PM_2.5 composition over 1989–2013 are highly consistent for PM_2.5 (−2.4 vs −2.4%/yr), secondary inorganic aerosols (−4.3 vs −4.1%/yr), organic aerosols (OA, −3.6 vs −3.0%/yr) and black carbon (−4.3 vs −3.9%/yr) over North America, as well as for sulfate (−4.7 vs −5.8%/yr) over Europe. Simulated trends over 1998–2013 also have overlapping 95% confidence intervals with satellite-derived trends in population-weighted mean PM_2.5 for 20 of 21 global regions. Over 1989–2013, most (79%) of the simulated increase in global population-weighted mean PM_2.5 of 0.28 μg m^–3yr^–1 is explained by significantly (<i>p</i> < 0.05) increasing OA (0.10 μg m^–3yr^–1), nitrate (0.05 μg m^–3yr^–1), sulfate (0.04 μg m^–3yr^–1), and ammonium (0.03 μg m^–3yr^–1). These four components predominantly drive trends in population-weighted mean PM_2.5 over populous regions of South Asia (0.94 μg m^–3yr^–1), East Asia (0.66 μg m^–3yr^–1), Western Europe (−0.47 μg m^–3yr^–1), and North America (−0.32 μg m^–3yr^–1). Trends in area-weighted mean and population-weighted mean PM_2.5 composition differ significantly