An automated method for thermal-optical separation of aerosol organic/elemental carbon for 13C analysis at the sub-µgC level: A comprehensive assessment.

We describe and thoroughly evaluate a method for 13C analysis in different fractions of carbonaceous aerosols, especially elemental carbon (EC). This method combines a Sunset thermal-optical analyzer and an isotope ratio mass spectrometer (IRMS) via a custom-built automated separation, purification, and injection system. Organic carbon (OC), EC, and other specific fractions from aerosol filter samples can be separated and analyzed automatically for 13C based on thermal-optical protocols (EUSAAR_2 in this study) at sub-µgC levels. The main challenges in isolating EC for 13C analysis are the possible artifacts during OC/EC separation, including the premature loss of EC and the formation of pyrolyzed OC (pOC) that is difficult to separate from EC. Since those artifacts can be accompanied with isotope fractionation, their influence on the stable isotopic composition of EC was comprehensively investigated with various test compounds. The results show that the thermal-optical method is relatively successful in OC/EC separation for 13C analysis. The method was further tested on real aerosols samples. For biomass-burning source samples, (partial) inclusion of pOC into EC has negligible influence on the 13C signature of EC. However, for ambient samples, the influence of pOC on the 13C signature of EC can be significant, if it is not well separated from EC, which is true for many current methods for measuring 13C on EC. A case study in Xi'an, China, where pOC is enriched in 13C compared to EC, shows that this can lead to an overestimate of coal and an underestimate of traffic emissions in isotope-based source apportionment.

Stable isotope ratio method for the characterisation of the poultry house environment.

Stable isotope analysis was applied to describe the poultry house environment. The poultry house indoor environment was selected for this study due to the relevant health problems in animals and their caretakers. Air quality parameters including temperature, relative humidity, airflow rate, NH3, CO2 and total suspended particles, as well as mean levels of total airborne bacteria and fungi count, were measured. Carbon isotope ratios (13C/12C) were obtained in size-segregated aerosol particles. The carbon (13C/12C) and nitrogen (15N/14N) isotope ratios were measured in feed, litter, scrapings from the ventilation system, feathers and eggs. Additionally, the distribution of δ13C and δ15N values in different tissues of the chicken was examined. The airborne bacteria and fungi extracted from the air filters collected from poultry farms were grown in the laboratory in media with known isotope values and measured for stable isotope ratios. Analysis of isotope fractionation between microorganisms and their media indicated the applicability of stable isotope analysis in bulk samples for the identification of source material. The analysed examples imply that stable isotope analysis can be used to examine the indoor environment along with its biology and ecology, and serve as an informative bioanalytical tool.

Stable isotopes measurements reveal dual carbon pools contributing to organic matter enrichment in marine aerosol.

Stable carbon isotope ratios in marine aerosol collected over the Southern Indian Ocean revealed δ13C values ranging from -20.0‰ to -28.2‰. The isotope ratios exhibited a strong correlation with the fractional organic matter (OM) enrichment in sea spray aerosol. The base-level isotope ratio of -20.0‰ is characteristic of an aged Dissolved Organic Matter (DOM) pool contributing a relatively homogeneous background level of DOM to oceanic waters. The range of isotope ratios, extending down to -28.2‰, is characteristic of more variable, stronger, and fresher Particulate Organic Matter (POM) pool driven by trophic level interactions. We present a conceptual dual-pool POM-DOM model which comprises a 'young' and variable POM pool which dominates enrichment in sea-spray and an 'aged' but invariant DOM pool which is, ultimately, an aged end-product of processed 'fresh' POM. This model is harmonious with the preferential enrichment of fresh colloidal and nano-gel lipid-like particulate matter in sea spray particles and the observed depleted δ13C ratio resulting from isotope equilibrium fractionation coupled with enhanced plankton photosynthesis in cold water (-2 °C to +8 °C). These results re-assert the hypothesis that OM enrichment in sea-spray is directly linked to primary production and, consequently, can have implications for climate-aerosol-cloud feedback systems.