Online aerosol carbon stable isotopic composition measurement
Carbon isotopes of CO2 (δ13C) can be used for understanding the natural and anthropogenic sources of carbon content of atmospheric aerosol. CO2 produced from different sources has different isotopic composition. For example, CO2 produced from fossil fuel burning has different isotopic ratio that in biomass burning produced CO2. Atmospheric aerosols are rich in organic carbon and elemental carbon which are derived from numerous sources such as vehicular emissions, coal and biomass burning. Atmospheric CO2 is fixed by C3 and C4 plants vio a ribulose bisphosphate carbodylase in photosynthesis and the isotopic ratio of carbon in these plants are different because of plants preference to lighter isotope (12C vs 13C). Thus plant has lower 13C / 12C ratios. The typical δ13C value of C3 plants is in the range of -23 to -30 0/00. Thus, δ13C could be used to distinguish C3 plants from C4 plants and the ratio becomes more useful to deduce the contribution of biomass burning to the organic carbon content of aerosols. This ratio acts as tracer of biomass burning and serves the same purpose as Levoglucosan, another biomass burning tracer species.
To increase the temporal resolution of stable isotopic composition of aerosol carbon, a tandem system was developed to connect Sunset OCEC with a cavity enhanced CO2 isotope online analyzer. The system supplies the exhaust from semi-continuous OCEC analyzer to the high precision and high resolution stable isotopic CO2 measurement and derives the aerosol carbon stable isotopic ratio online. The method provides a powerful tool for online detection of carbon isotopic composition in atmospheric aerosol for more accurate estimation of carbon sources from different reservoir.
Figure 1. Instrument setup