In this experiment the students will look at the effect of Particulate matter or other substances that have landed on ice and test how this can speed up the melting of ice by affecting its albedo. Particulate Matter and aerosols are made up of a variety of pollutants, some of them enhancing and some counteracting the greenhouse effect when they are in the atmosphere. But once they land on snow or ice, they will promote the melting of these surfaces.
Chemistry Curriculum Links AQA GCSE
9.2.3. Properties and effects of atmospheric pollutants
Particulate Matter is a pollutant that absorbs at many different wavelengths, some act as greenhouse gases and others actually reflect more light than they absorb, leading to a reduction in the temperature of the atmosphere. When they (or Black Carbon in particular) deposit on snow and glaciers, they change the albedo (the reflectivity) of the snow surface. This controls the heat balance at the surface of snow and ice surfaces as the darker colour of the ice will lead to it melting faster.
Particulate Matter is solid particles that are so small that they float in the atmosphere and can be measured as a concentration in the atmosphere. They are formed from incomplete combustion of wood and fossil fuels. PM smaller than 2.5 microns (2.5 x 10-9 m), PM2.5 , is much smaller than the width of a human hair and can enter into our lungs and be carried into the blood system and cause damage to the brain and the cardiovascular system.
Uncertainties to do with the quantities of the different particles in the atmosphere (and the fact that particles enhance cloud formation) are part of the biggest current uncertainty in climate models.
Class Practical
This experiment can be carried out in pairs or larger groups and takes about 20 minutes.
Follow the notes in the student worksheet, allowing more time to discuss what particulate matter is, what is albedo and how sunlight is absorbed differently by different coloured substances.
Discussion Questions
- Which ice cubes melted faster? Was it what they expected?
- Did all groups get similar results? Can we compare the melting rates as a % of original mass and see if they are similar between groups? What is the error in the melting rate of the 3 types of ice cubes?
- Does covering them with brown or black melt them faster?
- What are the possible errors in the experiment?
Application to the World’s Glaciers:
Glaciers around the world are more exposed to particulate matter now than they ever were before the industrial revolution and the increase in industry and cars over the last century. Covering snow and ice with a dark layer changes the albedo and they absorb more heat and melt quicker than the pure ice.
Particulates are tiny solid or liquid particles that are present in the atmosphere. They are sometimes termed aerosols when they float in the air. Examples are dust, spores and pollen, salt from sea spray, volcanic ash and smoke. Black carbon (elemental carbon (soot) or organic carbon) from incomplete combustion in the atmosphere can actually absorb incoming solar radiation and cool the Earth. However, when these particles land on ice, the absorption of radiation will enhance the ice´s melting.
References
Iain Stewart BBC black ice experiment
UN Environment programme, 2019: Glaciers are melting and air pollution is the cause
See bar chart of radiative forcing of various gases or particulates in Fig 14.4 Ramaswami et al., 2019
