| Abstract Title: | New 9λ Aethalometer model AE36s – Performance and advanced characterization of aerosol sources |
| Presenter Name: | Dr Asta Gregorič |
| Co-authors/Co-presenters: | Mr Gašper Lavrič Mr Viktor Pilko Dr Matic Ivančič Dr Irena J. Brecelj Dr Balint Alfoldy Dr Amalia Muñoz Dr Eduardo Yubero Dr Rok Podlipec Dr Martin Rigler |
| Company/Organisation: | Aerosol d.o.o. |
| Country: | Slovenia |
Abstract Information :
The Aethalometer is a widely used filter photometer capable of measuring black carbon concentration and light-absorbing properties of aerosol particles. In this study, we present the performance of the new Aethalometer model AE36s (Aerosol Magee Scientific), which addresses two crucial areas that have emerged in the scientific community in recent years: (1) the sensitivity of filter photometers to rapid changes of relative humidity, (2) the need for improved characterization of the absorbing part of organic aerosols in blue and UV region, the so-called brown carbon (BrC). Despite technical changes and improvements of the instrument, continuity of absorption measurements is essential; thus, in this study, we demonstrate the equivalence with AE33 through a series of laboratory and ambient measurement campaigns. To improve the characterization of BrC share of absorption in blue and UV regions, two additional wavelengths were introduced in the new Aethalometer model AE36s with respect to the older models: the 400 nm increases the resolution of absorption in a large gap of AE33 channels between 370 nm and 470 nm, whereas 340 nm extends the measurement range in the UV spectrum. The performance of AE36s above was evaluated and compared to its predecessor AE33 during long-term field campaigns conducted at an urban background site in Ljubljana (Slovenia), Milan (Italy), rural background site in Payerne (Switzerland) and at Hyytälä (Finland) regional background station. Slopes of the orthogonal regression for all common wavelengths are within 5% range relative to the unity with R2 > 0.99. Signal to noise ratio in the AE36s is also significantly improved, which results in more stable determination of the absorption Ångström exponent (AAE). Ambient measurements were compared with results obtained in the EUPHORE simulation chamber for different particle emission sources and ageing state. AAE was analyzed for the long (AAE590-950; 590-660-880-950 nm) and short spectral range (AAE400-520; 400-470-520 nm) separately, which allowed us to distinguish different absorption fingerprints. Chamber experiments have revealed significant absorption of BrC at 340 nm for fresh BrC emitted during the smouldering phase of biomass burning. In the first part of the aging phase, when the aerosol is exposed to sunlight, significant increase of absorption was observed in the middle wavelength range (470 – 660 nm), thus decreasing short range AAE400-520 and increasing long range AAE590-950. A slow decrease of absorption in the middle wavelength range follows with further photochemical ageing. Freshly emitted diesel exhaust and the flaming phase of biomass burning are characterized by lower BrC contribution and about 20% lower absorption at 340 nm than expected if AAE400-520 would be extrapolated to 340 nm. Validation of the new Aethalometer model AE36s has revealed significant improvement of signal to noise ratio and reduced sensitivity to rapid changes of relative humidity in comparison to its predecessor AE33. Additional wavelengths, 340 nm and 400 nm can be efficiently used to enhance the resolution of absorption spectral dependence and improve the characterization of Brown Carbon.
