This project was co-financed by Eurostars grant E!8296, coordinated by Aerosol d.o.o. and with Paul Scherrer Institute, PSI, as a scientific partner. The final result of this project lead to the Total Carbon Analyzer TCA08 and further to Carbonaceous Aerosol Speciation System CASS; and several scientific publications.
Aerosols, particulate matter (used here synonymously), are a hot topic in research concerning the anthropogenic impact on climate and the impact on human health and have thus significant societal impacts. We will develop a near-real-time instrument to measure the Total Carbon (TC) content of ambient fine particulate mass (PM), for field and laboratory use without the need for specialty gases. The carbonaceous fractions contribute 20-90% to PM. Carbonaceous fractions are considered to be much more toxic than the inorganic salts. The instrument will rapidly heat the PM sample to create a pulse of combustion products that are converted to CO2 and detected as a large transient increase above the ambient CO2 level. This explicitly eliminates the need for specialty carrier gases or pre-conditioning. Variation of analytical parameters offers dynamic ranging over several orders of magnitude, permitting use at remote or background sites as well as in heavily-polluted locations. This supports an alternative method for the separation of carbonaceous PM into Organic Carbon (OC) vs. Elemental Carbon (EC) fractions, but the TC measurement is not subject to the ambiguity of arbitrary threshold points. Measurements of Black Carbon (BC) by optical absorption with the newly developed Aethalometer AE33, and TC by total combustion can be calibrated against fundamental analytical standard materials for TC (CEN/TR 16243). The relation OC = TC – BC is used to assign the OC fraction. BC is related to EC since both analyses are relating to the same sample, examining different properties. The methodology offers a less complex design with reduced operational requirements making it an ideal candidate for a field deployable, automated, continuous monitoring application.
We propose an alternative method for the separation of carbonaceous aerosol samples into organic versus elemental fractions for consideration of equivalence to the existing OC/EC thermal methods. Existing OC/EC progressive-heating methods suffer from sample dependent pyrolysis (charring) artifacts; volatility dependence on the inorganic compounds in the sample; require precise optical alignment; demand precise temperature measurement and control; and use complex equipment that requires specialized carrier gases (Cavalli 2010).
Our proposed alternate method measures BC in particular and light absorbing carbon in general by optical absorption, for example with the newly developed Aethalometer AE33, and TC by flash combustion of the totality of the sample. The BC measurement can be related to photometric standards that are precisely defined, and can be related to EC by means of suitable intercomparison and definition. The TC measurement quantitates the entire sample without ambiguity of arbitrary separation, and can be calibrated against precisely-weighed analytical standard materials. Importantly, the proposed method is based on the measurement of fundamental physical/chemical properties of the carbonaceous aerosol while also being highly correlated to the thermal-optical methods, such as EUSAAR2, IMPROVE, or NIOSH (Cavalli 2010). The Real Time Carbon Analyzer (RTCA) has been specifically designed for operation either in the laboratory, for the analysis of previously-collected samples; or the same analytical chassis can be fitted with a flow system for on-line, continuous operation in the field. The combustion chamber is designed for practical field use: ease of access, service and maintenance. When coupled to the BC data stream from an Aethalometer, this analysis feature optimizes the TC performance. The two measurements will be combined within an interface to report BC, TC, OC and EC. This is all enabled by the innovative software features of the newly developed Aethalometer AE33 (Eurostars E!4825).
This TC-BC strategy eliminates the requirement for specialty gases and high electrical power, by creating an instrumental method that operates only on ambient air at low electrical power (about 500 watts); and eliminates the complexity, component count and maintenance requirements of progressive-heating units currently being marketed. The TC-BC combination can be implemented for off-line laboratory analysis of previously-collected samples; or on-line for real-time field use.
Total Carbon Analyzer TCA08
Carbonaceous Aerosol Speciation System CASS