1. Introduction Method Results Conclusions
In-plume secondary pollutants formation from the Greater Paris region and its impact on surrounding regions
Q.J. Zhang (1, 4), M. Beekmann (1), E. Freney (2), K. Sellegri (2), A. Schwarzenboeck (2), J.M. Pichon (2), A. Colomb (2), A. Borbon (1), V. Michoud (1), SAFIRE (3)
(1) LISA/IPSL, Laboratoire Interuniversitaire des Systèmes Atmosphériques, UMR CNRS 7583, Université Paris Est Créteil (UPEC) et Université Paris Diderot (UPD), France.
(2) Laboratoire de Météorologie Physique, Clermont-Ferrand, France
(3) Service des Avions Français Instrumentés pour la Recherche en Environnement, Toulouse, CNRS/INSU, de Météo-France et du CNES
(4) Currently at Aria technologies, Boulogne-Billancourt, France
Introduction
Method
The 9 bins Volatility-basis-set (VBS) approach (Robinson et al., 2007; Murphy and Pandis., 2009) to simulate the chemical aging of semi-volatile POA (primary OA) and IVOC (Intermediate volatility organic carbon), and the 4 bins VBS approach (Lane et al. 2008) for anthropogenic and biogenic SOA simulation (main precursors are aromatics and terpenes) have been integrated into the regional chemistry transport model CHIMERE.
These VBS approaches are applied to simulations of primary and secondary organic aerosol (POA & SOA) formation during the summer and winter MEGAPOLI campaign period within the Greater Paris region.
In the framework of the FP7 / EU project MEGAPOLI, an intensive campaign was launched in the Greater Paris Region in July 2009 and in January/February Its major objective was to quantify different sources of organic aerosol (OA) within a megacity and to better understand secondary aerosol formation. Organic aerosol (OA) is a major component of urban aerosol, but the contribution of different formation pathways is still difficult to quantify.
Model configuration for 2 nested domains
continental domain
( °N ; 10.5°W-22.5°E) with 0.5°x0.5° resolution
regional domain
( °N ; 0.35°W-4.41°E) with 3km resolution
Schematic representation of SOA formation
Single-step CSS
VBS
In this study, the regional CTM CHIMERE is evaluated with airborne measurements from the French ATR-42 research aircraft during the 1-month’s summer campaign. The impact of OA formation in the plume of the Paris agglomeration, a megacity of more than 10 millions inhabitants, is quantified.
For this aim, the Volatility-basis-set (VBS) approach was implemented into the CHIMERE air quality model.
Results
Comparison of observed and simulated secondary pollutants
OA contribution from Paris to its surrounding (from VBS-MPOLI)
Simulation configurations
CSS
VBS-T2
VBS-MPOLI
Emissions
EMEP/LA
MEGAPOLI
POA
Non-volatile
VBS
SOA
Single step
Monthly mean concentrations
The MEGAPOLI emission inventory (TNO) shows three times lower BC and POA emissions in the Paris agglomeration than the LA inventory (from Laboratoire d’Aérologie, Toulouse, France), however, larger values in the surrounding
POA
(µgm-3)
Anthropogenic origins
Oxidized POA (OPOA)
Anthropogenic SOA (ASOA)
Paris OA
(µgm-3)
Paris
Biogenic SOA (BSOA)
(µgm-3)
Paris
Flight 32, July 21st
Altitude=600m
BC plume: indicator of observed and simulated Paris plumes.
HNO3 vs. NH3
Simulation for 8 flights
Dots: witihin plume
Circles: outside of plume
Nitrate formation inside the Paris plume is under a NH3-controlled regime, while outside of the plume can also be under a HNO3-controlled regime.
The ratio HNO3/NH3 is about 1.4 inside the paris plume.
POA monthly averaged concentrations are relatively low of about 0.1 µgm-3 in the Paris agglomeration.
The highest concentration of OPOA up to 0.35 µgm-3 (produced regionally with background concentration of about 0.25 µgm-3 within 200km) is found in the NE of Paris region, which implies a delay of its formation from Paris emissions during days with important photochemical activity and southerly wind.
ASOA shows also a plume towards NE extending to more than 200km due to the same reasons as OPOA, which indicates an important impact of megacities to regional air quality.
During a NE continental wind regime, the plume extended towards SW. On the average over all flights an increase of about 0.45 µgm-3 at a distance of 150km is found.
In northern France around the Paris agglomeration, the gradient of monthly averaged OA concentration is NW to SE due to predominated westerly wind during the campaign and due to continental precursor emissions
The Paris OA plume is directed on the average towards E and NE.
Biogenic SOA shows important concentrations in the south and makes about 1 µgm-3 in the Paris region.
NO3 plume: Coincides with observed and simulated BC plumes:
NH3-controlled regime
Paris contribution OA
SOA
ASOA
Paris plume on July 16th
(µgm-3)
OA, 13h
Paris
OA, 22h
OA vs. Ox
OA plume: Coincides with observed and simulated BC plumes.
CSS underestimates the OA level and does not simulate an OA enhancement within the plume; the OA/Ox ratio is largely underestimated; => large underestimation of SOA production normalized by photochemical activity.
VBS-T2 and VBS-MPOLI simulations broadly agree with measurements
Important SOA formation
Relatively important background level over the flight pattern related to biogenic origin
Overestimated OA/Ox ratios by up to a factor of two from VBS-T2 and VBS-MPOLI, but still satisfying result when taking into account all uncertainties, such as OA volatilité, OA émissions, SOA yields, etc.
The ratio of the difference between VBS-MPOLI with and without Paris emissions and VBS-MPOLI with Paris emissions) shows that OA formation related with Paris emissions can extend to 0.08 (8%) at a distance of about 200km, mainly due to SOA formation during the transport, especially ASOA (up to 0.22, 22%) on a monthly average.
In Paris, there is 20% of SOA produced by its own emissions
For a particular Paris plume, for example on July 16th, OA concentrations increase by more than 10 µgm-3 due to SOA formation after transport from Paris of about 150km.
Extended OA levels can be transported to regions even farther away.
Conclusions
The VBS approach is integrated into a regional chemistry transport model CHIMERE, and the model simulations are evaluated with airborne measurements during the MEGAPOLI summer campaign in the Greater Paris region.
Nitrate formation related to the Paris emissions, is simulated under a NH3-controlled regime in the plume, while under both HNO3-control and NH3-control appear outside the plume.
In the plume, OA enhancement is well simulated when applying the VBS approach. The simulated OA/Ox slope is with a factor of two with respect to the observation, which means a relatively good simulations for the SOA formation from photo-chemical activities.
The monthly mean concentration of OA has a clear NW-to-SE gradient, due to continental emissions and prevailing winds, with the most important contribution from BSOA.
The OA contribution from Paris emissions (anthropogenic impact) to its surroundings is on the average of 8% at about 200 km distance from the agglomeration. However, in a given plume, enhanced OA levels are transported to much larger distances.
In future studies, CHIMERE will be also applied and analyzed with measurements during the winter campaign, as well as with available data over Europe, and other regions (China ?).
Acknowledgement: This research in the context of the MEGAPOLI project is financially supported by the European Community’s Framework Program FP/ under grant agreement n° Q.J. Zhang was supported by a PhD grant from the French CIFRE (ANRT) attributed to LISA and ARIA Technologies. Support from the French ANR project MEGAPOLI – PARIS (ANR-09-BLAN-0356), from the CNRS-INSU/FEFE and the Ile de France/SEPPE as well as from internal Max Planck Institute for Chemistry funds are acknowledged.