In situ, satellite measurement and model evidence on the dominant regional contribution to fine particulate matter levels in the Paris megacity

Abstract

A detailed characterization of air quality in the megacity of Paris (France) during two 1-month intensive campaigns and from additional 1-year observations revealed that about 70% of the urban background fine particulate matter (PM) is transported on average into the megacity from upwind regions. This dominant influence of regional sources was confirmed by in situ measurements during short intensive and longer-term campaigns, aerosol optical depth (AOD) measurements from ENVISAT, and modeling results from PMCAMx and CHIMERE chemistry transport models. While advection of sulfate is well documented for other megacities, there was surprisingly high contribution from long-range transport for both nitrate and organic aerosol. The origin of organic PM was investigated by comprehensive analysis of aerosol mass spectrometer (AMS), radiocarbon and tracer measurements during two intensive campaigns. Primary fossil fuel combustion emissions constituted less than 20% in winter and 40% in summer of carbonaceous fine PM, unexpectedly small for a megacity. Cooking activities and, during winter, residential wood burning are the major primary organic PM sources. This analysis suggests that the major part of secondary organic aerosol is of modern origin, i.e., from biogenic precursors and from wood burning. Black carbon concentrations are on the lower end of values encountered in megacities worldwide, but still represent an issue for air quality. These comparatively low air pollution levels are due to a combination of low emissions per inhabitant, flat terrain, and a meteorology that is in general not conducive to local pollution build-up. This revised picture of a megacity only being partially responsible for its own average and peak PM levels has important implications for air pollution regulation policies

Contributions of local and regional sources to fine PM in the megacity of Paris

“…It is noteworthy that PMCAMx/PSAT simulates that the relative contribution of sources in Paris to total PM 2.5 tends to be lower during polluted than during average days. This rather surprising result is consistent with the observation-based estimates of Beekmann et al (2014).…”

“…This underestimation of local sources (almost 0.2 µg m −3 for summer and winter) could be explained by the behavior of fresh POA. Both the measurement-based studies of Beekmann et al (2014) and Freutel et al (2013) found that almost 62 % of the OA in the center of Paris was HOA (Primary Organic Aerosol) and cooking OA and 38 % was oxygenated OA. The discrepancy between the measurements and the model can be explained by the cooking emissions which have not been included in the PMCAMx inventory used in this study.…”

“…Beekmann et al (2014) used measurements inside the center of the Paris and the surrounding areas to estimate what fraction of the particulate matter is local. The data were collected, during July 2009 and January to mid-February 2010 as a part of the MEGAPOLI intensive field campaigns (Beekmann et al, 2014). PM 1 concentration in Paris during summer was on average between 5.3 and 7.5 µg m −3 , but during winter was between 15.2 µg m −3 and 18.5 µg m −3 .…”

“…Zhang et al (2013) implemented the VBS approach into CHIMERE to simulate the behavior of organic aerosol and compared with measurements performed during the MEGAPOLI summer campaign (Baklanov et al, 2010). Beekmann et al (2014) used measurements inside the center of the Paris and the surrounding areas to estimate what fraction of the particulate matter is local. The data were collected, during July 2009 and January to mid-February 2010 as a part of the MEGAPOLI intensive field campaigns (Beekmann et al, 2014).…”

Sources and mixing state of summertime background aerosol in the north-western Mediterranean basin

“…A number of studies have reported that in rural environments in the Mediterranean, airborne PM and ammonium sulfate concentrations undergo a seasonal cycle characterised by a summer maximum (Bergametti et al, 1989;Kubilay and Saydam, 1995;Querol et al, 1998a, b;Rodríguez et al, 2001Rodríguez et al, , 2002. This seasonal cycle has not been reported at rural sites in central and northern Europe, where high PM events are mostly recorded in winter during stagnant episodes caused by cold temperature inversions and low wind speed (Beekmann et al, 2015;Favez et al, 2007;Monn et al, 1995;Röösli et al, 2001;Turnbull and Harrison, 2000). Long-term measurements at sites in the western and eastern Mediterranean basin by Querol et al (2009) showed that mineral matter is the major component of PM 10 (22-38 %) in both areas, with relatively high proportions in PM 2.5 (8-14 %), followed by sulfate, organic matter (OM), nitrate and ammonium.…”