Appendix : PARCS (PI K. Law LATMOS)

The main goal of PARCS (Pollution in the ARCtic System) is to improve understanding about the sources and fate of Arctic pollution and its impacts on climate, ecosystems and human society. Arctic pollution is highlighted a key priority in the French Chantier Arctique prospective as well as at international level by, in particular, the Arctic Council. PARCS addresses 4 major research objectives, using a multi-disciplinary approach, bringing together groups from 16 French labs with strong track records in several key Arctic research areas and complementary expertise. It aims to promote interactions between different disciplines working on air pollution (e.g. aerosols, ozone), climate (aerosol-cloud interactions), toxic contaminants such as mercury and persistent organic pollutants, impact on ecosystems (contaminants in seabirds, pollutant interactions with marine/snow environments), and societal impacts and risks (air pollution). PARCS focuses on a number of specific research actions including the collection of new data on pollution sources and risks to societies in Siberia, a region where data are greatly lacking, and data about pollution deposition and impacts on ecosystems and aerosol-cloud interactions, in critical areas where there are still major gaps in our understanding. These new datasets will be analyzed, together with existing data using a range of models with the aim to improve predictive capability of current and future changes in Arctic environment and ecosystems. PARCS also aims to promote coordination and. PARCS will make a major contribution to international initiatives, including a new international initiative on Arctic air pollution (PACES) being chaired/led by French scientists (under the International Arctic Science Council and International Global Atmospheric Chemistry (IGAC)/IGBP), and via continued participation in Arctic Council working/expert groups (Arctic Monitoring and Assessment Programme/AMAP; Conservation of Arctic Flora and Fauna/CAFF), Pan-Eurasian Experiment (PEEX)/Centre Franco-Siberian etc. It will also contribute to the new EU coordinationaction, EU-PolarNet.

PARCS addresses 4 major research objectives covering 1) improved characterization of local pollutant emissions relative to long-range pollution transport from mid-latitude sources, through a combination of new measurements, community based risk assessments and pollution monitoring, 2) better understanding about interactions between natural cycles and anthropogenic pollution, including pollutant wet/dry deposition, quantification of natural sources (relative to anthropogenic sources), and pollutant recycling at the snow/ice-atmosphere interface, 3) examination of pollutant deposition impacts on marine biogeochemistry, nutrients and oceanic emissions together with improved assessment of contaminant impacts on Arctic fauna (sea-birds), 4) improved understanding about aerosol-cloud interactions and direct/indirect effects on climate. These objectives will be tackled using data analysis and modeling and are linked through a common coordination strategy.

WP4: Aerosol and cloud processes impacted by Arctic pollution

Contributors: LATMOS (Raut), LaMP (Jourdan), LSCE, LOA

WP4 focuses on studying the interactions between pollution aerosols, clouds and their impacts on direct and indirect radiative effects in the Arctic, as they have been highlighted as a major uncertainty in climate models and are critical for understanding Arctic climate. The purpose is to understand how aerosols change cloud properties, and reciprocally how clouds remove aerosols through precipitation. The ultimate goal is improved assessment of the effects of how the surface radiation budget in the Arctic is affected by long-range pollution transport (reaching the Svalbard) and local sources in the Arctic (along Norwegian coasts). This strategy relies on a combination of analysis of existing and new aerosol and cloud data (Tasks 4.1/4.2), modeling activities (Task 4.3) as well as satellite data analysis.

Task 4.1: Impact of local pollution aerosols on CCN (cloud condensation nuclei) properties (LSCE, LATMOS, LOA, LaMP)

A focused campaign on local aerosol sources and clouds will be carried out in Norway in spring 2016when aerosol loads are important in the Arctic, precipitation is lsss efficient and cloud occurrences are high (Mioche et al., 2015). This campaign complements previous airborne efforts focusing on remote or natural aerosols or ground-based campaigns. Two ULAs will make flights of about 3hrs along the western coast of Norway (two weeks) and spend one additional week in northern Norway, in the vicinity of Tromsø. A truck will ensure the experiment logistics. One ULA, equipped with a micro Raman lidar (pointing downwards), UV and IR radiometers, will sample pollution from ship plumes along Norwegian coast from oil and gas platforms under sea breeze regimes and from different pollution sources in the vicinity of Tromsø: ships, domestic wood burning, transport of pollution from the Kola Peninsula. It will allow retrieval of aerosol optical depths pollution plumes in the lowest layers (< 3km). The second ULA will carry an optical particle sizer (GRIMM + CPC) to investigate fine particles in pollution plumes, a small nephelometer to retrieve the aerosol scattering coefficient. This ULA will fly in polluted layers detected by the lidar to analyze the microphysical and optical properties of aerosols from different sources. It will be equipped with Frequency Modulated Continuous Wave cloud radar, pointing upwards to determine the reflectivity and Doppler velocity in clouds layers overcasting the aerosol plumes, providing quantitative information on the low stratiform clouds in northern Norway. The combination of the ULA lidar and radar measurements is very promising as it gives high-resolution horizontal and vertical sampling of both aerosol and cloud microphysical and optical properties. We have also requested funds from U. Saclay for an additional week (to account for poor weather) and to add further instrumentation (see section 6). 

Satellite observations will be used to extend the study at larger scale. Observations from CALIOP/CloudSat will be used to perform a statistic analysis of satellite data to better constrain theindirect effects of aerosols in particular aerosol impacts on ice nucleation and precipitation (snow or rain) processes. We will build on recent approaches (e.g. Coopman et al., 2014) to consolidate results through multi-year analysis and better describe the effect of various aerosols types on clouds depending on a careful constraint for meteorological conditions. Our analysis will be validated locally through combined use of satellite information and field measurements performed in this project, and extended to the pan-Arctic using regional modeling. In particular, POLDER and MODIS will provide observations of aerosol properties (effective radius, layer altitude and aerosol optical depth) above clouds that are complementary to the ULA observations taken below clouds. In addition, cloud properties such as geometric thickness, altitude and liquid microphysics can be retrieved from space. This will enable an estimation of aerosol forcing under clear/cloudy skies and enable a comprehensive description of microphysical and radiative interactions between clouds and aerosols in the Arctic.


Outcomes: (i) Improved quantification of local pollution impacts on aerosols/clouds in the Norwegian Arctic, including diurnal cycle and spatial heterogeneity of radiative fluxes and on pan-Arctic scale; (ii) Assessment of pollution aerosol impacts from different sources on potential cloud nuclei.


Task 4.2: Characterization of aerosol-cloud processes in a pristine region (LaMP, LOA, LATMOS)

Data on aerosol-cloud interactions along the Norwegian coast will be complemented by a groundbased campaign at Mount Zeppelin (Svalbard), a relatively clean region impacted episodically by longrange pollution to study the formation, persistence, and microphysical properties of clouds (esp. cloud phase distribution) and direct/indirect effects. In particular, mixed phase clouds (MPC) can persist for several days and cover large swaths of the Arctic region. They occur as single or multiple stratiform layers of super-cooled droplets near the cloud top from which ice crystals form and precipitate. These clouds and especially the liquid layers they comprise have a large impact on the surface radiative fluxes There, cloud microphysical and optical properties, such as cloud phase distributions, crystal habits and particle size distribution will be sampled in situ to better document the microphysical processes occurring in Arctic clouds. The instrumental set up will benefit from a previous ground based campaign performed at Mount Zeppelin in 2012 (CLIMSLIP-Ny Alesund) showing that the accurate measurements of aerosol, cloud droplet and ice crystal concentrations as well as liquid-ice partitioning, for instance, are critical to understand the complex web of process interactions occurring in MPC. Accordingly, a new set of in situ cloud instruments (Cloud Particle Spectrometer with Polarization Detection, Polar Nephelometer, 2D-S imaging probe, Cloud Droplet Probe, PVM Gerber) and remote sensing devices (BASTA cloud Radar and ceilometer) as well as aerosol measurements for the characterization of the IN (ice nuclei chamber) and CCN properties complemented by aerosols chemical properties from filters will be deployed at the Zeppelin Station (Ny-Alesund) in spring 2017. Data from this campaign will also complement data collected on pollutant deposition (WP2).



(i) Characterization of impact of CCN/IN properties of Arctic aerosols on cloud properties; (ii) Improve knowledge of liquid-ice partitioning at small-scale and impacts on cloud optical and radiative properties; (iii) Better understanding of aerosol composition and cloud droplet freezing mechanisms responsible for formation and persistence of Arctic clouds in clean region impacted by long-range of pollution.


Task 4.3: Improving modeling of aerosol-cloud interactions and their impacts on aerosol radiative effects (LaMP, LATMOS)

The representation of mixed phase clouds properties and aerosol-cloud interactions are poorly constrained in state-of-the art models. Model simulations at regional scale using bulk microphysics (WRF-Chem) or using detailed microphysics (DESCAM) will be constrained using existing and new PARCS in-situ and remote sensing observations. More specifically, the impact of aerosols from local sources on ice nuclei (IN) and cloud condensation (CCN) populations, ice phase initiation reported from in-situ measurements in Svalbard, and liquid water content profiles close to the cloud top assessed from satellite observations, will be used to validate and improve current microphysics scheme in the DESCAM model. A new parameterization of droplets and ice crystal formation derived from this detailed model will be provided to the mesoscale WRF-Chem model. This will lead to improved assessment of direct/indirect radiative effects of aerosols on the surface energy budget in the European Arctic using WRF-Chem. We also aim to evaluate the impact of pollution aerosols on marine/terrestrial ecosystems both in terms of earth-surface radiative (UV) fluxes and estimation of dry/wet deposition fluxes of aerosols, including soot (linked to WPs 2/3), which remain very poorly constrained in models.


(i)Improved parameterization of CCN and IN in the Arctic; (ii) Improved quantification of direct and indirect effects of local/remote aerosols in the European Arctic, (iii) Modeled estimates ofdry and wet deposition fluxes of aerosols in Norwegian coastal and Svalbard regions.