Determinación de atributos relevantes y construcción de escenarios

Anthropogenic emission trends in aerosol primary and precursors during the last 50 years has resulted in considerable regional changes in ambient PM2.5

air quality. Findings reported in Chapter 3 showed that simulated changes in ambient PM2.5, using the HadGEM3-UKCA CCM, generally followed that

of long-term regional observations highlighting pronounced declines across high-income regions of North America and Western Europe with associated growth across many low and middle-income regions, particular across Asian countries. These findings are consistent with declining emissions associated with air quality regulation and emission control technology implementation in high-income regions to that of emission growth associated with popula- tion and economic expansion at the expense of equivalent regulation and control in many low and middle-income regions over the past 50 years. Re- gional disease burdens attributable to ambient PM2.5exposure generally fol-

lowed that of regional changes in ambient PM2.5, with an estimated increase

in global burden of disease of between 89% to 124% in 2009, relative to 1960. This global attributable mortality increase which was largely driven by mor- tality growth in Asia, the growth of which was strongly influenced by de- mographic transitions (i.e., population growth and ageing), highlighting the

6.4. Summary and synthesis 161

importance of this transition when considering future near-term disease bur- den trends. However, more importantly, the results reported in Chapter 3 highlight the advantages of clean air policy for improving air quality and public health in North American and European regions. This provides the evidence base needed for policy makers across polluted low and middle- income regions can learn from and replicate. However, given the non-linear disease exposure-responses relationships associated with highly polluted re- gions (i.e., high exposure distributions) and near-term projected transitions in demography, low and middle-income countries may need to introduce very stringent ambient air pollution standards in order to replicate similar public health benefits experienced by high-income regions since the 1960s. Although not specifically addressed in Chapter 3, much of the anthropogenic emission declines experienced across high-income regions, particularly West- ern Europe, were a result of declines in residential solid fuel combustion, typically coal for heating. This use and reduction in use of solid fuels, in part due to combined air quality policy, economic and energy transitions, shares some parallels with energy poverty and transitions facing many low and middle-income countries today. For example, while combustion of solid fu- els are generally less important for anthropogenic emissions in high-income countries today, they remain an important fuel source across many low and middle-income regions, where 3 billion poor people still rely on such fuels (e.g., biomass and coal) to meet basic energy demands (e.g., cooking, heating and lighting). At the same time, although the global number of poor house- holds using solid fuels has decreased over the last few decades, population growth has kept the total number of users at relatively stable levels. As a result, the residential sector remains an important anthropogenic emission source in the present-day, undoubtedly leading to large global and regional negative impacts on public health and the wider environment. For poor com- munities in low and middle-income, the use solid fuel clean cookstoves or

clean fuels, such as LPG, is considered one of the best ways to reduce emis- sions from residential solid fuel combustion, potentially leading to large pub- lic health benefits through improved household and ambient air quality, and additional climate and socio-economic co-benefits. However, until relatively recently, little was known about the overall impact of residential emissions on air quality, health and climate in the present-day. Understanding these impacts are a vita first step in identifying where clean cookstoves and fuels will have the most benefit, and was the focus of Chapter 4 of this thesis. Us- ing the TOMCAT-GLOMAP CTM, results reported in Chapter 4 showed that residential emissions contributed substantially to regional annual mean sur- face PM2.5, BC and POM concentrations in the present-day, with significant

contributions across regions of Asia and Sub-Saharan Africa, as well as many Eastern European countries of the former Soviet Union. The disease burden due to the removal of residential emissions was estimated to be consider- able (3.0 to 0.5 million deaths globally), highlighting the potentially large public health benefits of residential emission controls, even when consider- ing a number of key emission uncertainties. Understanding the present-day radiative impacts due to residential emissions, however, was shown to be uncertain and sometimes of opposite sign. This uncertainty was in part due to the limitations of using a offline radiative transfer model together with uncertainties associated with residential emission mass flux, size and com- position, and other uncertain model parameters, highlighting the need for more advanced modelling approaches and measurements.

The last chapter of this thesis (Chapter 5) was designed in such away that would naturally lead on from Chapters 3 and 4. In particular, it focused on understanding the possible impact of changes in anthropogenic emissions on future near-term air quality and disease burdens in 2050, with an ad- ditional focus on clean emission technologies, particularly residential clean

6.4. Summary and synthesis 163

cookstoves, as a means of reducing impacts by 2050. Using the TOMCAT- GLOMAP CTM, Chapter 5 showed that despite ambient PM2.5 concentra-

tions declining many regions (apart from South Asia and to some extent Sub-Saharan Africa) under a reference scenario, the attributable global bur- den of disease increased by 73% in 2050 (relative to 2015). Similar to the findings reported in Chapter 3, the growth in the mortality burden was sig- nificantly influenced by demographic transitions, so much so that disease burden increases were estimated in regions where ambient PM2.5concentra-

tions had declined relative to 2015 (e.g., China). This finding further high- lights a real need for polluted regions to adopt stringent limits on ambient PM2.5 in order to reduce disease burdens in the near-term. Relative to this

reference scenario, the widespread implementation of clean residential com- bustion technologies (i.e., clean cookstove) was found to improve near-term air quality and public health benefits in 2050, especially for many low and middle-income countries, such as Sub-Saharan Africa. The adoption of clean cookstove technologies alone was found to represent one half to two thirds of the maximum preventable ambient PM2.5and mortality estimated across

Sub-Saharan African countries in 2050. At the global level, clean residential technologies were found to represent 20% of global the preventable PM2.5

mortality in 2050. The findings reported in Chapter 5 thus highlight the po- tential effectiveness of residential emission controls and technologies for im- proving near-term ambient air quality and public health, particularly among many low and middle-income regions, where they can also help towards al- leviating many other environmental and socio-economic problems.

While the results reported in thesis represent a first step in identifying im- pacts and potential areas of interested for policy, the section below provides a discussion on additional work that could be undertaken to build on what is reported here. Additionally, a further discussion is also provided below on research priorities for the wider research community.