AE36 Aethalometer: Performance Demonstration and Application of Black Carbon Index
MARTIN RIGLER, Matic Ivančič, Bálint Alföldy, Irena Ježek Brecelj, Asta Gregorič, Aerosol d.o.o.
Abstract Number: 468
Working Group: Carbonaceous Aerosols
Abstract
The recommended guidelines for particulate matter (PM2.5 and PM10) issued by the World Health Organization (WHO, 2021) have been reflected in the updated directives of the Environmental Protection Agency (EPA) in the United States and the European Union. Specifically, the annual mean concentration for PM2.5 has been reduced to 9 µg/m³ in the United States and 10 µg/m³ in the European Union. Under the extant standards in Europe, less than 1% of the population is exposed to air with PM2.5 concentrations exceeding the prescribed limits. However, this proportion escalates to 97% when evaluated against the WHO guidelines. To be able to further decrease PM2.5 concentrations, mitigation strategies must be targeted to specific sources, and source apportionment needs to be implemented in monitoring networks. Carbonaceous aerosols (CA) contribute significantly to the PM2.5 mass concentration. Additionally, black carbon (BC), in particular, which is highlighted as a good practice statement in 2021 WHO guidelines, has been associated with a range of adverse health effects, including respiratory and cardiovascular diseases, cancer, and even birth defects.
The Aethalometer is a widely used filter photometer capable of measuring the light-absorbing properties of aerosol particles, especially BC. In this study, we present the performance of the new Aethalometer model AE36 (Aerosol Magee Scientific), developed to meet the needs of the monitoring community. The performance of new Aethalometer has been significantly enhanced by redesigning the filter compartment, which is now robust to changes in relative humidity (RH). The AE36 is designed for long-term unattended operation, facilitated by a new self-cleaning procedure and a 20m filter tape. The communication of pollution levels to the public has been simplified with the implementation of a Black Carbon (BC) index, which is a proprietary measure of air quality based on Black Carbon concentrations. BC index follows the principle of Air Quality Index determination. It relies on the linear interpolation method of BC concentration applied between pre-set boundaries of BC index categories (Fung et al., 2022):
BC index=(Ihigh-Ilow)/(BC24,high -BC24,low)•(BC24-BC24,low)+Ilow,
where BC24 is the 24 hour running mean of hourly averaged BC concentration, BC24,low and BC24,high are the lower and upper limit of the index category, and Ilow, Ihigh are the corresponding index values. The performance of AE36 with improvements mentioned above was evaluated and compared to its predecessor AE33 during a long-term field campaigns at an urban background and remote sites. 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.