Black carbon and aerosol optical property
measurements at a midsize city in Po valley, Italy
Fenjuan Wang
1*, Giulia Pavese
2, Roberta Vecchi
3, Giovanni Lonati
1,
Senem Ozgen
1, Stefano Cernuschi
11Department of Civil and Environmental Engineering, Politecnico di Milano, Milan, Italy
2 National Council of Research - Institute of Methodologies for Environmental Analysis, Potenza, Italy
3 Department of Physics, University of Milan, Milan, Italy *Email: fenjuan.wang@polimi.it
Conclusions
Comparison of black carbon measurements obtained by two methods was performed at Piacenza Italy using an absorption photometer (MAAP) and two Aethalometers (AE31, AE51). The results show that equivalent black carbon (EBC, Petzold et al., 2013) concentrations recorded by the three instruments follow a similar trend with pronounced morning and evening peaks during rush hours. The regression analysis shows that the EBC raw levels measured by MAAP and AE51 are quite similar, whilst AE31 overestimated EBC about 10-15% compared to MAAP and AE51 records. Apart from local emissions, air mass origins also have a detectable effect on the black carbon and particle optical properties in Piacenza.
Methods
During the UPUPA measurement campaign in Piacenza in September 2011, black carbon was measured by a Multi Angle Absorption Photometer (MAAP 5012), an Aethalometer AE31 and a Micro Aethalometer AE51 and inter-comparisons were conducted. Optical columnar properties of aerosols were also measured by Ocean Optics S2000 radiometer. Aerosol Optical Depth (AOD), Angstrom extinction parameter (alpha) and aerosol components were analyzed to investigate particles optical and microphysical properties and their origin, supported by back trajectories calculation.
Relationship of EBC levels by MAAP, AE31 and AE51
The average EBC raw concentrations are 3686±136 ng/m3 by MAAP,
4404±166 ng/m3 by AE31 and 4185±144 ng/m3 by AE51. Scatter plots
show correlations between the 3 instruments higher than 0.9, and not influenced much by the size of the dataset. The regression indicates that AE31 overestimates EBC concentration about 10-15% compared to
MAAP and AE51. When the EBC concentration is lower than 1st quartile or
higher than 3st quartile more difference are recorded by MAAP and AE31.
For the larger dataset (N = 1751), R2 is 0.305 when EBC concentration is
less than 2 µg/m3. R2 is 0.708 when EBC is larger than 5 µg/m3.
References
Petzold et al., Atmos Chem Phys, (2013) 13: 8365-8379.
Figure 2. Temporal variations of PM10 (daily average), EBC (daily average by AE31), AOD (aerosol optical depth, daily averaged columnar data from 8 AM to 3 PM).
EBC and optical properties
Figure 2 shows that the lowest levels of PM10,
EBC and AOD on September 20th and 21st, when
the air masses were from the Atlantic Ocean, as shown in Figure 4, with high loading of water soluble ions. Maximum values observed on
September 28th correspond to air masses from
Eastern Europe, with higher particle loading of aged urban emissions and increased fraction of BC. The different aerosol origin has also been reflected by the relationship between AOD and Angstrom extinction parameter.
Figure 3. Scatter plots, linear regressions and EBC 5-min raw concentration distributions for the simultaneous datasets. (EBC1: MAAP, EBC2: AE31, EBC3: AE51)
Figure 4. Backward trajectories ending at Piacenza measurement site or Sept. 20th 2011 (left) and for Sept.
28th 2011 computed by NOOA Hysplit Model
EBC 2 EBC 1 EBC 3 EBC 2 EBC 1 N = 185 hours y = 1.129x ‐320.7 R² = 0.957 Y= 1.019x + 426.8 R² = 0.930 y = 1.192x + 9.868 R² = 0.955
EBC1 EBC2 EBC3
Date September 2011 9.19 9.20 9.21 9.22 9.23 9.24 9.25 9.26 9.27 9.28 9.29 9.30 PM1 0 (u g/m 3) 10 15 20 25 30 35 40 45 E BC (ng/m 3) 2000 2500 3000 3500 4000 4500 5000 A O D(7 80) 0.0 .1 .2 .3 .4 .5 .6 PM10 EBC AOD(780) EBC1 EBC2 N =1751 y = 1.153x + 252.6 R² = 0.902 N = 482
Figure 1. Measurement site at Piacenza, Italy (TR site - 45.056570° N, 9.706234° E ).
