Short statement of the objectives

Formaldehyde (HCHO or H₂C=O) is the most abundant of the carbonyl compounds in the atmosphere. It is also the smallest member of the aldehyde family. Formaldehyde is found both in the remote background atmosphere and in polluted urban atmospheres. The photooxidation of hydrocarbons invariably generates HCHO in the atmosphere (Finlayson-Pitts and Pitts, 1986; Atkinson, 1994). In the background troposphere, where methane concentration is considerably higher than that of non-methane hydrocarbons (NMHC), methane is the dominant formaldehyde precursor. Close to the surface, local sources of NMHC also become important in producing HCHO. In processes similar to that for methane, formaldehyde is generated from the oxidation of biogenic hydrocarbons, such as isoprene and terpenes (Levine, 1984) and from the oxidation of anthropogenic hydrocarbons. Formaldehyde is also anthropogenically generated directly from incomplete combustion processes, both from biomass burning (Holzinger et al., 1999) and from internal combustion engines. The figure below shows some of the reactions involved in the oxidation of hydrocarbons via HCHO to CO.

Through its subsequent decomposition by photolysis and reaction with the OH radical, formaldehyde serves as a source of the hydroperoxyl radical (HO₂) and carbon monoxide (CO). In producing HO₂, HCHO affects the partitioning of odd hydrogen radicals. As a source of CO, HCHO plays an important role in the global budget of CO in the natural troposphere (McConnel et al. 1971). In both cases, HCHO exerts an influence on the oxidising capacity of the atmosphere (Lelieveld and Crutzen, 1990).

Most important to atmospheric chemistry is the formation of HO2 with its subsequent involvement as an oxidant, in O3 formation and in OH production (Logan et al., 1981; Jacob et al., 1995).

Accurate HCHO measurements are thus important in constraining and validating photochemical models of the troposphere, in understanding the budgets and cycling among various reactive species and the global budget of CO. Despite this importance and the relatively large number of techniques employed, there is still considerable uncertainty in ambient measurements of HCHO. In various intercomparison campaigns, the level of agreement varies from good to quite poor (Cárdenas et al. 2000; Gilpin, 1997, and references sited therein).

It is therefore of importance to obtain a better understanding of the differences between the various measurement techniques and try to reduce the disagreement between these various techniques. This will be of great value both to validate atmospheric chemistry models and to validate satellite measurements of HCHO.

Photochemical smog is one of the most, if not the most, serious air pollution problem in Europe today. Episodes with high concentrations of ozone and NOx cause harm to human health and to vegetation. Abatement of such pollution is one of the biggest challenges to environmental authorities, both nationally and at the Community level. There is a clear need for better scientific tools to understand the mechanisms behind the formation of photochemical smog. Better tools are also needed to predict and warn the population against such pollution. The photographs below show typical smog episodes over the Po Basin in northern Italy.

How to meet the objectives?

FORMAT consists of six main workpackages (WPs) (plus coordination) with the following verifiable objectives:

1. The Ground based measurements of HCHO WP will quantify the amounts of formaldehyde in the troposphere at selected sites in the Po Valley during two field deployments. Several different and independent measurements techniques will be used and one will intercompare these different techniques. A verifiable objective is how well the experimental methods compare.
   
2. The Airborne measurements of HCHO WP will use data taken from various aircraft to obtain information on the vertical distribution of HCHO from the ground up to approx. 5 km altitude. The various instrumental techniques will be compared. A verifiable objective is how well the experimental methods compare.
   
3. The Measurements of additional species WP will collect data on other important species, such as other carbonyls, NOx, VOC, meteorology, atmospheric optical properties so that the formaldehyde results can be interpreted. A verifiable objective will be the amount of data collected and how these data help in improving our knowledge of the mechanisms for formaldehyde formation.
   
4. The Atmospheric chemistry modelling and intercomparison with observations WP will assemble data on HCHO for the last five years from European networks. These data will be compared with output from a regional and a global 3D CTM. The regional CTM will also be used in forecast mode as a support to the two campaigns. Verifiable objectives will be to what extent one can reproduce the observations and to what extent one is able to pin down the reasons for the discrepancy between modelled and observed HCHO.
   
5. The Satellite data WP will use data from GOME and SCIAMACHY and compare these to model results and measurements. The satellite retrieval algorithms will be further developed and improved. A verifiable objective will be how well satellite data compare to groundbased and airborne measurements and modelled formaldehyde.
   

The Benefits and recommendations WP will summarise the results of the other WPs and come up with recommendations for how smog episodes can be better forecasted based on the new knowledge acquired through the FORMAT project. There will also be an activity on the socio-economic benefits of the project. Verifiable objectives will here be how precise recommendations that can be made for satellite retrievals and modelling and how precise it is possible to estimate the socio-economic benefits of the project.