A novel model evaluation approach focusing on local and advected contributions to urban PM<sub>2.5</sub> levels – application to Paris, France

Abstract

Abstract. Aerosol simulations in chemistry transport models (CTMs) still suffer from numerous uncertainties, and diagnostic evaluations are required to point out major error sources. This paper presents an original approach to evaluate CTMs based on local and imported contributions in a large megacity rather than urban background concentrations. The study is applied to the CHIMERE model in the Paris region (France) and considers the fine particulate matter (PM 2.5 ) and its main chemical constituents (elemental and organic carbon, nitrate, sulfate and ammonium), for which daily measurements are available during a whole year at various stations (PARTICULES project). Back-trajectory data are used to locate the upwind station, from which the concentration is identified as the import, the local production being deduced from the urban concentration by subtraction. Uncertainties on these contributions are quantified. Small biases in urban background PM 2.5 simulations (bias of +16 %) hide significant error compensations between local and advected contributions, as well as in PM 2.5 chemical compounds. In particular, winter time organic matter (OM) imports appear strongly underestimated while local OM and elemental carbon (EC) production is overestimated all along the year. Erroneous continental wood burning emissions and missing secondary organic aerosol (SOA) pathways may explain errors on advected OM, while the carbonaceous compounds is likely to be related to errors in emissions and dynamics. A statistically significant local formation of nitrate is also highlighted from observations, but missed by the model. Together with the overestimation of nitrate imports, it leads to a bias of +51 % on the local PM 2.5 contribution. Such an evaluation finally gives more detailed insights on major gaps in current CTMs on which future efforts are needed.

Simulation of fine organic aerosols in the western Mediterranean area during the ChArMEx 2013 summer campaign

“…The overestimation of secondary organic aerosol with the CHIMERE standard scheme is a new feature (Bessagnet et al, 2008 ;Hodzic and Jimenez, 2011 ;Petetin et al, 2014). A previous comparison of CHIMERE with organic aerosol simulations using the same scheme and coupled to MEGAN biogenic emissions, resulted in a good close to the western Mediterranean basin (Montelibretti, Italy).…”

“…The CHIMERE model has been previously validated for different parts of the world Solazzo et al, 2012 ;Borrego et al, 2013 ;Berezin et al, 2013 ;Petetin et al, 2014 ;Rea et al, 2015 ;;Konovalov 30 et al, 2015 ;Mallet et al, 2016). The data set presented in section 3 is used for model validation.…”

“…The CHIMERE model ; http://www.lmd.polytechnique.fr/chimere) is an offline regional CTM 5 (Chemistry-Transport Model) which has been tested rigorously for Europe and France (Zhang et al, 2013 ;Petetin et al, 2014;Colette et al, 2015;Menut et al, 2015 ;Rea et al, 2015). It is also widely used in both research and forecasting activities in France, Europe and other countries .…”

Evaluating BC and NO<sub><i>x</i></sub> emission inventories for the Paris region from MEGAPOLI aircraft measurements

“…On average, the NO x regional background roughly accounts for 15-25 % and 15-30 % of the levels in Paris for observations and simulations, respectively. From 1-year measurements during the PARTICULES campaign (Bressi et al, 2013), it has been found that the BC regional background contributes to about a third to the annual BC urban background average in Paris, and that this fraction is probably underestimated by the CHIMERE model (Petetin et al, 2014). However, this uncertainty source remains difficult to quantify more precisely.…”

Oligomer formation in the troposphere: from experimental knowledge to 3-D modeling

“…As a consequence, air quality models (AQMs), despite significant progress, still have difficulties to quantitatively reproduce the observed particulate matter (PM) levels and gradients, and continue to underestimate the formation of SOA in the troposphere, from cities to remote areas (Shrivastava et al, 2011;Ervens et al, 2011;Petetin et al, 2014). In this regard, the chemistry of organics in the aqueous condensed phase remains poorly characterized.…”