10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Urban Aerosol Size and Concentration: Characterization in a Light Industrial Area 2017/2018 Compared to 2005
TORSTEN TRITSCHER, Thomas Krinke, Axel Zerrath, Oliver F. Bischof, TSI GmbH
Abstract Number: 1513 Working Group: Aerosol Physics
Abstract The particle size distribution of urban aerosols is typically dominated by ultrafine particles (UFP) originating from local sources such as traffic and industrial emissions. Due to their negligible mass they are clearly underrepresented by legislative PM10 mass measurements. This is one reason why the UFP contribution to urban air quality is better characterized by their number size distribution and particle number concentration.
In 2005 we carried out an initial study of the physical properties of the urban aerosol in a light industrial area in the city of Aachen, Germany (Bischof & Zerrath, AAAR 2005). The sampling location was near a freeway and in close proximity to two bus depots operating the local public transport network. We chose to repeat that study 12 years after the original campaign as the larger of the two bus companies frequently made upgrades to their bus fleet. This change in one of the predominant local emission sources should be notable in urban air quality improvements when comparing our latest measurements to the 2005 results. One interesting additional fact is that the city of Aachen introduced a low emission zone (LEZ) in February 2016. Other studies have shown (TROPOS, 2017) that improvements in air quality due to LEZ’s are not well reflected when only considering PM10, while UFP measurements easily show reductions well in double digit values.
During both studies the sampling site was located at an identical distance of 50 m from the road and 200 m from the freeway. The depot of the public transport company and the lots of the private bus depot remained in their locations. Both result in extended bus traffic passing by the sampling location in particular in the mornings and afternoons of weekdays. We used a complete sampling system with PM10 head, PM1 cyclone, Nafion dryer and flow splitter in order to condition the ambient air aerosol and allow the connection of a wide choice of instruments.
An Ultrafine Particle Monitor (UFP, TSI Model 3031) was used to measure the particle number size distribution in 6 size fractions ranging from 20 to 800 nm. The UFP monitor was complimented by a high-resolution SMPS (TSI Model 3938) during selected periods. In addition we operated two models Condensation Particle Counters (CPC): a butanol-based monitoring CPC that fully complies with the CEN/TS 16976 specifications (TSI Model 3772-CEN) and a water-based instrument (WCPC, TSI Model 3788).
For the duration of the 2005 measurements the particle number concentration was typically below 5,000 particles/cm3 at night time but exceeded values of 10,000 particles/cm3 during day time with occasional peaks of up to 100,000 particles/cm3. We found that these peaks correlated well with the bus fleet leaving from or arriving at the bus depot. Particle size distributions were dominated by particles below 200 nm in diameter and individual events with traffic revealed modal values of the distribution below 50 nm.
The influence of traffic remains clearly visible also in the 2017 data. Especially the morning peak when buses leave the depot showed a typical behavior, with the size distribution being dominated by particles smaller than 70 nm. The difference in total particle concentration between the UFP monitor and the CEN-CPC can be mainly attributed to the different lower cut-off size of 20 nm and 7 nm, respectively. We will present more detailed data, including measurements made during other months to complete the characterization of the urban aerosol at this site.