Spatiotemporal Heterogeneity of Lung-Deposited Surface Area in Zurich Switzerland: Lung-Deposited Surface Area as a New Routine Metric for Ambient Particle Monitoring

Objective: To assess the spatiotemporal heterogeneity of lung-deposited particle surface area concentration (LDSA), while testing the long-term performance of a prototype of low-cost-low-maintenance LDSA sensors. One factor hampering epidemiological studies on fine to ultrafine particles (F-to-UFP) exposure is exposure error due to their high spatiotemporal heterogeneity, not reflected in particle mass. Though LDSA shows consistent associations between F-to-UFP exposure and health effects, LDSA data are limited. Methods: We measured LDSA in a network of ten sensors, including urban, suburban, and rural environments in Zurich, Switzerland. With traffic counts, traffic co-pollutant concentrations, and meteorological parameters, we assessed the drivers of the LDSA observations. Results: LDSA reflected the high spatiotemporal heterogeneity of F-to-UFP. With micrometeorological influences, local sources like road traffic, restaurants, air traffic, and residential combustion drove LDSA. The temporal pattern of LDSA reflected that of the local sources. Conclusion: LDSA may be a viable metric for inexpensively characterizing F-to-UFP exposure. The tested devices generated sound data and may significantly contribute to filling the LDSA exposure data gap, providing grounds for more statistically significant epidemiological studies and regulation of F-to-UFP.


Station Name
Site theme Station surroundings Elevation (m asl)

Reckenholz (L4000) Rural
Station is located on a office building with farms around; 270 m south of major road; 1.6 km north of minor road; the sensor is on the roof of a building ~460 ~20 Brütten (remote (L4002)) Rural Station is minimum 4 km from any major roads with farms around; a power distribution system and office of responsible supplier in close vicinity: the sensor is on the roof of a building ~597 8.5

Rümlang (L4006) Rural
Station is next to a star gazing observatory, with a major road ~650 m S, minor road ~150 m N, and the Zurich airport ~2.4 km NE ~500 1.5

Kloten Feld (L4003) Suburban
Station is next to sport and farm fields, residential buildings to the west with small factories within the town; ~ 400 m from major roads running N to NW, 660 m from Zurich airport (N); E to SW are buildings and a minor road; airport arrival flights fly over this location between 20:00 and 23:30 on weekends, and between 21:00 and 23:30 on weekdays ~444 4.5

Dübendorf (L4004) Suburban
The station is located next to a research facility with offices, small wastewater treatment plant; major roads (a primary road W and motorway, N) close by; and residential areas are also within the neighbourhood; a large construction site shares borders with the station; there is also a local small airport 1.2 km E,

Schimmelstrasse (L4007) Urban
The station is on a the side of a busy street junction with a major connecting road leading to the highway; the station is partly shielded by adjacent buildings with restaurants, offices and residential properties and next to a small parking lot, across from the station is a local train station. ~415 ~3.7 Rosengartenstrasse (L4008) Urban/major road The station is surrounded by residential buildings, and on the side of a busy major road The station is in the city centre, within a partly closed square with access paths and small streets primarily for pedestrians; food trucks and mobile restaurants are often present within the square, less than 50 m from the sensor. In the neighbourhood of the square are shopping centres, restaurants, and bars as the square is within a tourist destination.

Stampfenbachstrasse (L4009)
Urban (City centre) The station surrounded by school buildings, businesses, residential buildings, restaurants and hotels and on the side of a minor road with tram lines. The sensor was located at about 4 m above ground and next to the kitchen window of a pizzeria. SI. Figure S1 qualitatively shows the applicability of the LDSA devices in capturing the temporal variability in particle concentration during a co-location campaign before the deployment for the 2021-2022 campaign. There is very good agreement in time and changes in intensity between the LDSA devices and the particle counter, which are not depicted in the particle mass metrics. Mean LDSA in SI Figure 1 is the mean of the 10 devices deployed at one location (Kaserne) for about a month. The variability in the measurements across these devices were very small (bands depict 3 times standard deviation), with the relative standard deviation of.
SI. Figure S1. After a year's deployment without maintenance, one device was damaged, and most devices had problems with flow readings due to clogging of flow meter. Flow within the deployed prototypes was controlled by a fan, whose fan current was monitored. With the measured fan current and calibration of the flow to the fan duty cycle, naneos developed a flow correction factor for the devices. Without this flow correction, the relative standard deviation across these devices was 7.3%; with the flow correction, the relative standard deviation was 4.3% (SI Figure 2 (right)). The prototype devices have been updated to avoid such flow problems. Previous precision was recovered upon fixing the flow issues in the devices (not shown here). SI. Table 2a and Table 2b. presents the statistics on the LDSA concentrations observed during co-location measurements before and after the long deployment.