Table 4.

Summary of health, climate, emissions, and ecosystem issues related to sulphate, black carbon, and ozone

	Main human sources	Measurement	Toxicology	Epidemiology (mortality)	Climate	Ecosystems	Control
Sulphate particles	Power plants, industry, and transport from sulphur in fuels; concentrations falling worldwide	Little ambiguity, although emissions are mainly sulphur dioxide, complicating calculation of extent and location of transformation	Pure sulphate not shown to be toxic at concentrations encountered in the environment	Could have larger relative effects than undifferentiated fine particles that seem to be independent of other pollutants; sulphur dioxide, the emitted precursor, probably has additional effects	Generally cooling with some difference by location and complexity when in mixtures	Acid precipitation is of little uncertainty, but wide difference in effect by location	Control of sulphur dioxide has some, but not large interaction with other types of control
Black carbon particles	Household solid fuels, industrial coal, forest/grassland burning, and diesel from incomplete combustion; fossil-fuel proportion falling slowly	Basic measurement methods and metrics in some confusion across disciplines	Pure EC not very toxic in human and animal studies at environmental levels	Measured as EC, might have larger effects than undifferentiated fine particles, but results are not stable when other pollutants are included in models	Major uncertainties, but high warming potential that is complicated by location, short life, and mixtures with other aerosols	Melting and warming effects if it falls on ice or snow, particularly in Arctic and Himalayas; not yet well understood	Controls also reduce organic carbon emissions, which are generally cooling; net climate effect thus varies depending on source OC/BC ratio
Ozone (tropospheric)	Precursors: methane and NMVOCs with combustion and non-combustion sources and NOx mainly from combustion; concentrations rising worldwide	Ozone itself has little uncertainty, but precursor emission measurements are uncertain; might be formed far from sources; needs sunlight to form	Oxidative stress and inflammation pathways established for toxicity of pure ozone at or near environmental concentrations	Might have mortality effects that are independent of major types of small particles; evidence is more extensive for short-term exposure, but results from one large cohort study26 suggest much larger effects from long-term exposure	Warming potential well established, but total effect shared across precursor emissions in complex ways	Adversely affects agriculture and ecosystems; might reduce carbon storage	Complex atmospheric chemistry determines importance of VOCs vs NOx control locally

As noted in the text, epidemiological methods are not able to identify the mortality effects of the pure material in the environment, but rather the mixture of pollutants for which each material is an indicator. See panel for more details on climate interactions. EC=elemental carbon. OC=organic carbon. BC=black carbon. NMVOC=non-methane volatile organic compounds. NOx=nitrogen oxides. VOC=volatile organic compounds.