7. Accountability y control social
3.1 Cuestionario inicial acerca de la decisión social
Studies in the North America and Eastern Asia have highlighted the predominance of sulphate and OM in the sub-micron aerosol mass. Little input from ammonium nitrate aerosol to the accumulation mode mass has been shown in such studies, ex-cept in the vicinity of Mexico City (e.g. DeCarlo et al., 2008; Kleinman et al., 2008).
A major observation of the European-based studies is the significance of ammonium nitrate, particularly under polluted conditions in North-Western Europe (e.g. Schaap
et al., 2002; Putaud et al., 2004; Abdalmogith and Harrison, 2005; Koelemeijer et al., 2006) and in the Po Valley region (Schaap et al., 2002; Crosier et al., 2007a). Such observations are a consequence of the changing emission footprints in these different regions of SO2, NOx and NH3. Several modelling studies (e.g. Bauer et al., 2007;
Pinder et al., 2007; Makar et al., 2009) have noted that changes in ammonia emissions result in substantial changes in ammonium nitrate concentrations. Substantial emission reductions have occurred in Europe, particularly over the past 20 years, with relative reductions in SO2emissions decreasing by 66% from 1990-2005 (Monks et al., 2009).
Reductions in NOx(32%) and NH3(23%) have been much less pronounced over this period, due to differences in source distributions, abatement measures and reduction efficiency (Monks et al., 2009). The emission reductions in the United States were less pronounced than in Europe, while in Eastern Asia, emissions increased (Monks et al., 2009). Reductions in SO2emissions were particularly pronounced in Western Europe, which reduced emissions by 60-80% (Monks et al., 2009). Such relative changes in aerosol precursor emissions have a direct impact upon the aerosol chemical composi-tion in Europe, as the reduccomposi-tions in SO2emissions and associated particulate sulphate result in a greater availability of NH3to form ammonium nitrate in the particle phase.
Furthermore, the noted emission changes in Europe are liable to occur in other pol-luted regions both at present and in the future. This is indicated by the contribution of ammonium nitrate to pollution episodes in California, which has long been known (e.g White and Roberts, 1977).
The present study will explore the contribution of ammonium nitrate to the aerosol burden and its resultant climate impact in Western Europe. Ammonium nitrate is par-ticularly relevant to studies of the aerosol direct effect as a result of its large light scattering potential and affinity for water uptake. Furthermore, its formation pathways are a prime example of how the vertical distribution may impact upon the aerosol ra-diative affect. Ammonium nitrate formation is dependent on the vertical mixing state of the atmosphere (Neuman et al., 2003; Morino et al., 2006). It often forms at the top of the boundary layer as a consequence of partitioning of gaseous NH3and HNO3
to the particle phase. This partitioning process is biased towards the particle phase at lower temperatures. As a result, the formation of the particulate mass occurs in an area of greater relative humidity; thus the aerosol formed will be larger in size due to additional water uptake. Consequently, the resultant aerosol is likely to significantly perturb the radiative balance in such circumstances. Representation of the vertical dis-tribution of aerosols is a significant deficiency in current numerical models (e.g. Easter et al., 2004; Textor et al., 2006; Isaksen et al., 2009), thus such a phenomenon is of particular relevance. Ammonium nitrate is often not included in global and regional aerosol models (e.g. Myhre et al., 2006), as a result of the complexity of representing semi-volatile components and its interaction with both coarse and fine mode aerosol.
Such an omission could have major implications for regional weather and climate in
Western Europe, where ammonium nitrate has been shown to be an important con-stituent of the aerosol burden. Consequently, this study will attempt to characterise the controlling features related to the spatial distribution of ammonium nitrate in Western Europe and its resultant optical and radiative impacts.
This study will focus upon these key questions related to ammonium nitrate across Europe:
1. How much does ammonium nitrate contribute to the European aerosol burden and what modulates this contribution?
2. How important are its semi-volatile properties in terms of its vertical distribu-tion?
3. What is the impact of ammonium nitrate upon the European AOD field and re-sultant direct radiative effect?
Chapter 4
Papers
4.1 Overview of ADIENT and EUCAARI-LONGREX experiments
The present study mainly draws upon data associated with two major scientific re-search programmes; the European Integrated Project on Aerosol Cloud Climate and Air Quality Interactions (EUCAARI, Kulmala et al., 2009) and the UK Aerosol Prop-erties, PRocesses And InfluenceS on the Earth’s climate (APPRAISE).
EUCAARI is an EU Framework 6 Integrated Project focussing on aerosol particles and their effect on regional air quality and climate. EUCAARI brings together the leading European research groups, state-of-the-art infrastructure and key players from third countries to investigate the role of aerosol on climate and air quality. The stated objectives for the EUCAARI project are as follows:
1. Reduction of the current uncertainty of the impact of aerosol particles on climate by 50% and quantification of the relationship between anthropogenic aerosol particles and regional air quality, and
2. Quantification of the side effects of European air quality directives on global and regional climate, and provide tools for future quantifications for different stakeholders.
One aspect of EUCAARI was a major airborne intensive operation period which took place during May 2008. This period involved utilisation of multiple airborne plat-forms and long-term sampling at a variety of ground-based locations across Northern Europe. Two parallel airborne studies were conducted during this period and were known as the EUCAARI-LONG Range EXperiment (EUCAARI-LONGREX, hence-forth referred to as LONGREX) and the Intensive Observation Period at Cabauw Tower (IMPACT). The BAe-146 took part in the LONGREX campaign in conjunction with
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Mace Head
Puy de Dome Cabauw
Jungfraujoch Oberpfaffenhofen
Melpitz Vavihill
K-puszta Hyytiala
Cranfield
Figure 4.1: Location of relevant ground-based sites associated with ADIENT and LONGREX. Cranfield and Oberpfaffenhofen represesent the principal bases of op-eration for ADIENT and LONGREX respectively. The other ground-based locations represent the locations of major instrument deployments during the LONGREX flying period associated with the EUCAARI programme.
the Deutsches Zentrum für Luft-und Raumfahrt (DLR) Falcon 20-E5 (e.g. Wandinger et al., 2002). The aim of the project was to measure the distribution of aerosol over Europe via utilisation of airborne in-situ and remote sensing measurements. The gen-eral strategy for each flight was for the Falcon to fly at high altitude ahead of the BAe-146 using remote sensing LIDAR to derive on-line profiles of the tropospheric column. Such information could then be used by the BAe-146 to target areas suitable for in-situ sampling, generally at low-level. The IMPACT experiment centred around a ground-based measurement tower at Cabauw, in the Western Netherlands. Airborne measurements during IMPACT were provided by the French ATR-42 and an Airborne Cloud Turbulence Observation System (ACTOS), which was suspended from a heli-copter which operated during the campaign. IMPACT focussed upon cloud-aerosol interactions in the vertical column above Cabauw, with additional operations in the North Sea off the Dutch coast. Cabauw formed one part of a network of ground sites across Europe which included an extensive suite of aerosol and other atmospheric mea-surements. The locations of these are shown in Figure 4.1. The Falcon and BAe-146 performed several overpasses and vertical profiles over Melpitz, Cabauw and Mace Head during the course of the campaign.
APPRAISE is similarly interested in the impact of aerosol particles on climate as the central aspect is upon understanding atmospheric aerosols in order to improve mod-els of likely climate changes, with particular emphasis on regional scales. One aspect of APPRAISE was the Appraising the Direct Impacts of Aerosol on Climate (ADIENT) project, which aimed to provide information and understanding of the properties and processes that determine aerosol radiative properties and impacts. This encompassed a range of spatial scales, from individual plumes up to the regional scale of continental Europe. The key objectives of ADIENT were as follows:
1. Improved quantification of the key parameters controlling the evolution of the single scattering albedo and radiative effect of key aerosol types.
2. Assess the relative contribution of primary and secondary aerosol to the global aerosol burden and their subsequent effects on the radiative budget.
3. Assess the regional variability of aerosol and their effects.
4. The provision of an initial framework for assessments of the climatic impacts of air quality regulation of particulate material.
The LONGREX campaign formed the broader regional scope of ADIENT, conse-quently they are heavily linked in terms of their aims and scope. The following papers will present results and discussions related to the broad aims of these projects. Specif-ically, this will include the properties, processes and climate impacts of atmospheric aerosol across Europe.