Application of isotopes in the investigation of particulate matter (PM)

Besides the typical climate-relevant greenhouse gases like carbon dioxide, methane, nitrogen oxides (N₂O, NO_x), especially particulate matter (PM), e.g. aerosols and dust material, occupies a double-position in its effect on nature and on humans, on our health. The ongoing discussion in the media about the emission of such climate-relevant compounds by traffic, by industry and agriculture has significantly extended public awareness. Thus it is so much important to understand these processes using innovative methods. Stable and radioactive isotopes [1,2] are such tools which can assist us to explore the role and sources of PM in our environment.

Two teams have taken care of the topic, and the outcome of their investigations is now published in this issue. Andrius Garbaras and his colleagues [3] studied the apportionment of aerosols (PM₁) in urban and rural areas in and near Vilnius and presented their results at the European Society on Isotope Research (ESIR) Conference 2017. They revealed that traffic emissions in urban and rural areas comprise 26 and 15%, respectively, irrespective of the season. An important factor for the carbon distribution is the atmospheric transport path: Fuel-derived carbon was transported from highly industrialized Western European regions to urban and rural areas of Lithuania in both seasons, and additional carbon was emitted in the urban Vilnius area. The contribution of coal burning carbon in PM₁ was traced to private households and to energy production (from Poland, see also [1]). The authors demonstrated that the combination of stable carbon isotope ratio with radiocarbon data allowed distinguishing different carbon (fossil and non-fossil) sources in aerosols.

Elizabeth Romero-Guzmán and her team [4] investigated ratios of uranium and thorium radionuclides in PM₁₀ from the anthropogenically highly impacted centre of Mexico City and from the rural side Cuernavaca. They compared the specific radioactive concentrations in PM₁₀ with those in PM_2.5 and found enriched concentrations in PM₁₀. The uranium isotope ratios pointed clearly to an anthropogenic origin (nuclear reactor). An interesting result is the age dependence of the annual inhalation exposure of ²³⁴U and ²³²Th for three public groups with the highest for the adult group. Despite the inhalation of radionuclides in PM₁₀, a potential human health risk could not be found by this study.

Both articles point to further intensive investigations of particulate matter using stable and radioactive isotopes. We hope that these articles will find their interested readers and could motivate teams of isotope researchers.