The impact of climate change on air quality was the title for this year’s Environmental Chemistry Group Symposium, which incorporated the ECG’s 2006 Distinguished Guest Lecture and was held at Burlington House on March 1st.
The symposium was opened by Hugh Coe (Manchester University) who spoke on Aerosols, air quality and climate. After sketching out the nature of the anthropogenic forcing of climate change, Dr Coe drew attention to the uncertainties which exist in our understanding of aerosols - both in relation to climate change and in terms of their immediate effects on health and habitat.
Aerosols cause around 10,000 premature deaths each year, and they are also responsible for acid deposition on poorly buffered soils and for nitrification of low-nutrient habitats. Current areas of atmospheric aerosol research, which are being vigorously investigated in response to demands for climate change predictions at a regional scale, include:
the importance of the rate of growth (temporal decreases in number density matched by an increase in average particle mass);
the nature of the organic matter associated with aerosols;
and the role of the carbonaceous material present in aerosols.
Guang Zeng (University of Cambridge) talked on the Global modelling of chemistry and climate interactions. She described the use of the Meteorological Office’s Unified Model 4.5 to develop a view of climate in 2100. Using predictions of:
changes in vegetation (biogenic emissions);
and increases in anthropogenic emissions in a scheme involving 60 reactive species in 170 gas phase photochemical reactions,
Guang has been able to predict changes in tropospheric ozone and nitrogen dioxide over the next hundred years.
Her work showed that the oxidising capacity of the atmosphere would change chiefly due to increased biogenic emissions (e.g. isoprene) and changes in relative humidity, but also linked to changes in soil–NOx emissions. Changes in land-atmosphere interactions were identified as significant and in need of further assessment and understanding.
This year’s Distinguished Guest Lecture was given by Mike Pilling (University of Leeds) who was also the first recipient of the ECG DGL Medal. His lecture was entitled Climate change and air quality - a chemist’s perspective. Prof. Pilling pointed out that even though substantial reductions in air pollution emissions had occurred since the 1970s (primary PM10 and NOx emissions have decreased), increasing attention was now being given to secondary PM10 formation and long distance ozone transport and formation. For instance, emissions from the US cause an 0.5 ppb(v) a year increase in background ozone as measured at Mace Head.
There will also be important effects caused by predicted temperature increases on tropospheric pollution. Summer heat waves like those of 2003 will become the norm in 2040 (in 2003 there were1500 excess deaths in France of which 30% were due to air pollution).
Ultimately issues such as these can only be fully understood by establishing chemical mechanisms (MCMs: Master Chemical Mechanisms) with comprehensive kinetic data and by comparing simulated outputs with those from smog chambers and field measurements.
Simulations and predictions of the chemical effects of climate change require more precise and complete data from experimentalists for successful MCM modelling. For example, many organic compounds are conveyed into the free troposphere from the boundary layer by strong convective fronts. This transport requires the determination of rate constants over a large temperature range (down to 220 K). Such rate constants can be measured by laser flash photolysis. The ‘hypothetical’ reaction mechanisms can then be tested in smog chambers (e.g. the heavily instrumented chambers in Valencia), and comparisons made to field experiments.
In the case of transatlantic ozone transport, such field experiments were carried out by taking measurements from four aircraft flying along and across the New York ozone plume as part of a programme of “multiple interceptions of New York polluted air masses”.
As far as understanding the chemistry of climate change is concerned, Prof. Pilling used the example of methane to illustrate the uncertainties that exist in predicting the effects of climate change on atmospheric methane concentrations – changes in the atmospheric oxidative capacity (atmospheric OH radical concentrations) are particularly salient and uncertain.
Prof. Pilling concluded his presentation by explaining the importance of isoprene chemistry as global temperature increases, and describing changes that may occur in PAN chemistry, which would affect PAN’s role as a reservoir for nitrogen oxides.
This sequence of lectures provided an integrated and extensive overview of climate change chemistry. The speakers were expert and their expositions were given with great clarity. The capacity audience benefited from both these attributes.
Dr LEO SALTER
Royal Society of Chemistry Environmental Chemistry Group