Particulate matter and climate

Particulate matter is a mixture of solid particles and liquid droplets found in the air. Particles in the air affect climate because they absorb solar radiation to differing degrees and can affect cloud formation.

Black carbon, as its name suggests, is the strongest light absorber among components of particulate matter. It is a by-product of incomplete fuel combustion. Understanding the role of black carbon in climate change is one of the important challenges facing the research community and was the impetus behind the EU-funded project 'Chemical and optical properties of black carbon particles' (CHEMBC).

Scientists in the CHEMBC project are taking advantage of state-of-the-art aerosol instrumentation and data analysis techniques. Single-particle mass spectrometry is one of very few methods available to determine the black carbon mixing state in ambient environments. Researchers are investigating the sources of black carbon and its chemical processing during atmospheric transport that change its capacity to scatter and absorb solar radiation.

Researchers developed and applied new data mining techniques to convert mass spectral data to quantitative single-particle composition information for the first time. The method enabled apportionment of black carbon sources in Paris, France into freshly emitted local sources and aged particles transported from outside the city. The first ever application of information-theoretic entropy and diversity measures to single-particle composition enabled quantitative assessment of mixing on a scale of 0–100 %.

A novel data mining approach was developed to assess the tendency of ambient black carbon particles to accumulate atmospheric water based on single-particle mass spectral data. Conventionally, the analysis is applied to the bulk aerosol. In CHEMBC, the propensity of every single particle to form new clouds has been assessed for the first time.

CHEMBC is making an important contribution to both the accuracy of climate models as well as the ability of policymakers to make informed decisions. The role of carbon black in climate has become somewhat clearer, and the methods and techniques developed promise to shed light on other climate-related phenomena as well.