GAW Report No. 205 - IGAC Project

CHAPTER 1 - INTRODUCTION1.5 SCIENTIFIC TOOLS FOR STUDYING AIR POLLUTION IN MEGACITIESOne of the main challenges in addressing the impacts of megacities on the environmentand human health is the interaction of different spatial scales. Traditional problems of urbanizationinclude local to regional air quality and health issues. Scientific tools have been developed to coverlocal to regional scales at appropriate spatial and temporal resolutions. However, given their largeand increasing emission strength, megacities can also have effects on the global scale, which canonly be assessed by tools with global coverage. Global coverage, however, usually implies a lossof detail. The study of megacity impacts, both in terms of air quality and climate, thus necessitatesthe development and use of scale-bridging observations, emission inventories, and modelling.1.5.1 Ground-based, ship, and aircraft observationsGround-based observation networks are crucial for studying atmospheric chemistry inmegacities. In particular, continuous ground-based meteorological networks are essential in orderto characterize meteorological processes that control air pollution transport and stagnation events.In addition, year-round ground-based observation networks of atmospheric pollutants can detectexceedances of air quality standards, identify trends, detect or quantify emission sources, anddetermine the effects of air pollution control measures. Several examples of long-term groundbasedobservation databases of different spatial coverage are the AIRBASE database throughEIONET (http://air-climate.eionet.europa.eu/databases/airbase), the EBAS database hosted byNILU Norway (http://ebas.nilu.no/), and the AirParifdatabase for Paris (http://www.airparif.asso.fr/).In addition, many regulatory agencies in developed and developing countries have air pollutionmonitoring networks that provide hourly concentrations of important air pollutants such as O 3 , SO 2 ,NO X , PM 10 , etc. The number of air pollution monitors within a city and the air pollutants measuredvary greatly. A more globally consistent air pollution monitoring network would provide a robustdataset to study atmospheric chemistry in megacities and the environmental and human healthimpacts of air pollutants.More recently, surface “super-sites” have been incorporated into megacity field campaignsto complement and extend observations from aircraft and satellites. Super-sites providesimultaneous measurements of a variety of chemical and meteorological parameters and tend tohave more specific scientific purposes than long-term ground-based observation networks. Forexample, a series of super-sites may be used to study the chemical composition of air parcels or ofparticles as a function of time and location. Some examples of data from super-sites are therecent MEGAPOLI [http://megapoli.dmi.dk/] and MILAGRO[http://www.eol.ucar.edu/projects/milagro/] campaigns that focused on Paris, France and MexicoCity, Mexico respectively.In addition to surface super-sites, field campaigns in megacities often include aircraft andships that provide highly sophisticated platforms for studying atmospheric chemistry. Suchplatforms include in-situ and/or remote sensing instrumentation that provides observations ofprimary pollutants, secondary species, meteorological conditions, vertical profiles, and a widerange of other parameters. An airborne research platform provides a unique way to study thesource region, vertical and horizontal dispersion, and chemical and physical transformation ofatmospheric pollutants. Meanwhile, ship platforms provide the means to study meteorological andchemical processes at the surface ocean-atmosphere interface and in the marine boundary layer,which are regions difficult to measure using ground-based and aircraft observations, see Chapter 7for further details.The type of platform and instrumentation used to study atmospheric chemistry is dependenton the unique characteristics of the megacity of interest. Ground based, aircraft, and shipobservations often provide a very detailed local to regional view of air pollution. Therefore, there isa need to integrate observations from field campaigns and monitoring networks in order to bridgescales from a local to regional to global level. Such integration would enhance the globalperspective of the impacts of air pollution from megacities while still maintaining the critical detailedlocal and regional information.14