A pollution cloud obscuring Korea and the Sea of Japan in November 2001.

Kulmala is the director of both a national and a Nordic Centre of Excellence, both aiming to clarify the mechanisms involved in the generation of atmospheric aerosols. Measurements extend over exceptionally long time series. There are three Stations for Measuring Ecosystem – Atmosphere Relationships (SMEAR) in Finland. They are situated at three locations with different types of environment: one in the metropolitan area of Helsinki, one in Hyytiälä in the middle of a rural landscape, and one at Värrö, in Lapland. Generation of new atmospheric particles is being detected in Finland and abroad. The group collects particle data from field measuring stations ranging from Lapland to North Africa. The measurements are analyzed to determine the amounts of aerosols and the chemical composition in the atmosphere, as well as cloud generation physics.

An ammonia-sulfuric acid-water cluster. It is important for aerosol research to investigate how these clusters are generated. In addition to water, atmospheric particles usually contain sulfuric acid and ammonia. Detecting such particle formation at the molecular level is impossible, and complex calculation methods and powerful computers are needed to study them. A particle  keeps growing when new molecules attach to it. The growth process of aerosol particles turning into cloud droplets is one of the most significant issues in climate change research. The picture shows an ammonia molecule, with nitrogen depicted in blue, sulfur atoms in yellow, hydrogen in red, and oxygen in white.

Simultaneously, activities occurring, for example, in forest ecosystems and soil are also monitored. The precondition for this research is having the competence and computing capacities available to process massive data. Kulmala’s group combines interdisciplinary  competence in physics, chemistry, biology, and atmospheric science, and utilizes simulations and model development on a broad scale.

The group’s model development is cartain ried out together with the Finnish Meteorological Institute and CSC. Models describing the climate system are used to investigate the present, past and future climate, and climate change. Simulations are used to study the state of the climate system under changing conditions. These include changes in, for example, ocean currents and outgoing back-radiation, by taking into account complex interactions between the atmosphere, the oceans, soil and solar radiation, etc.

In the whole world there are not very many climate research groups utilizing modeling on different scales, ranging from a model of individual particle generation to a global ecosystem model. Through conversion mechanisms from gas into particles (nucleation mechanisms) gas molecules generate nanoclusters. Two or more gas molecules can bind with these clusters. These nanoclusters can be generated as a result of one or more mechanisms.

The cluster keeps growing caused by heterogeneous (surface) nucleation and/or condensed organic gas molecules. When they are big enough, their growth aided by vapors starting to condense and particles merging, the aerosol particles serve as cloud droplet nuclei. The effect of aerosols on the properties of air mass can be studied by using the Lagrangian Multiplier Method, in which experimental and simulated particle concentrations are compared when air mass from a clean area (such as marine air) reaches a particle forming impurity area. This comparison helps to understand how particle formation affects the concentration of cloud droplets and other properties of air masses. The information gained by using this method will make it possible to improve process descriptions for use on a wider scale in global models.

Global ecosystem models are used to investigate, among other things, the extent of radiative forcing caused by aerosols, and the effect of particles on cloudiness and precipitation. It is necessary to investigate aerosol formation in a global model, because reactions taking place in the atmosphere and their significance depend largely on regional conditions. However, global models have often limiand tations regarding efficiency; if the size of the climate model grid box is 200 km x 200 km, and if simultaneously we wish to investigate particles at a nanometer scale and their effects on the ambient atmosphere. By improving the efficiency of our models we can make the grid boxes smaller, which will bring out the regional conditions and properties.

This will make it easier to compare particle generation processes with real conditions within a specified grid box. ■

More information

http://cosmos.enes.org/
http://www.atm.helsinki.fi/indexeng.html
http://www.atm.helsinki.fi/eucaari/
http://www.csc.fi/english/research/sciences/geo
Theo Kurten’s academic dissertation: Quantum Chemical Studies on Tropospheric Nucleation Mechanisms Involving Sulfuric Acid: https://oa.doria.fi/handle/10024/13118