1. Introduction Perfluorocarbon Tracer Experiments on a 2 km Scale in Manchester Showing Ingress of Pollutants into a Building J C Matthews 1, M D Wright 1, A Bacak 2, H G Silva 1,3, M Priestley 2, D Martin 1, C J Percival 2 & D E Shallcross 1 1 Atmospheric Chemistry Research Group, School of Chemistry, Cantock’s Close, Bristol, BS8 1TS, UK. 2 Centre for Atmospheric Science, School of Earth Atmospheric and Environmental Sciences, University of Manchester, Manchester, M13 9PL, UK. 3 Renewable Energies Chair and Institute of Earth Sciences, University of Évora, Portugal Tel: +44 (0)117 3317042, email: j.c.matthews@bristol.ac.uk [1] Martin, D., et al. (2010). Atmospheric Science Letters 11 241-248 [2] Ren, Y., Schlager, H. and Martin, D. (2014) Chromatographia 77 309-316. [3] Simmonds, P. G., et al. (2002) Atmospheric Environment 36, 2147-2156.. [4] Pasquill, F and Smith, F. B., (1983). Atmospheric Diffusion. Ellis Horwood Ltd., Chichester. Funding for this work was provided by NERC Grant No. NE/J009008/1 and Leverhulme Trust Research Project Grant RPG-2014-102 and. MP is funded by a NERC Ph.D. studentship. HGS was funded by the Portuguese Science and Technology Foundation (FCT) through Grant SFRH/BPD/63880/2009. The authors wish to thank University of Manchester staff and students who assisted in measurements. Cyclic perfluorocarbons (PFCs) have been used to measure the passage of air in urban and rural settings as they are chemically inert, non-toxic and have low background concentrations. The use of pre-concentrators and chemical ionisation gas chromatography enables concentrations of a few parts per quadrillion (ppq) to be measured in bag samples [1]. Three PFC tracers were used in Manchester, UK in the summer of 2015 to map airflow in the city and ingress into buildings: perfluoromethylcyclohexane (PMCH), perfluoro-2-4-dimethylcyclohexane (mPDMCH, in 2 isomers; mc-PDMCH and mt- PDMCH) and perfluoro-2-methyl-3-ethylpentene (PMEP). A known quantity of each PFC was released for 15 minutes from steel canisters using pre- prepared PFC mixtures. Release points were chosen to be upwind of the central sampling location (Simon Building, University of Manchester) and varied in distance up to 2.2 km. A 3D sonic anemometer on the roof of a nearby University of Manchester building provided wind information. Samples are taken for 30 minutes into Tedlar bags, starting at the same time the as PFC release. For building measurements, receptors were placed inside the buildings on different floors; outside measurements were achieved through a sample line out of the window. Three of the sample positions inside the Simon Building were paired with samplers outside to allow indoor-outdoor comparisons. Bag samples were analysed using a gas chromatograph and mass spectrometer with a preconcentrator, in the atmospheric chemistry labs [2, 3]. Experimental methods Acknowledgements Conclusions References Figure 1. (a) typical release position with sonic anemometer and (b) sampling position during the campaign Tracer ReleasedDescriptionFloor1344 mg PMCH 394 mg mc-PDMCH 333 mg PMEP 1Simon BasementRoomInB NS 2Gas CageStreetOutGnd 6.04NS2.13 5Simon Balcony LabRoomIn2 NS 6Simon Balcony LabInletOut2 NS 8Simon OfficeRoomIn4 8.36NS 9Simon OfficeInletOut4 NS 10Simon Computing LabRoomIn6 NS 11Simon Computing LabInletOut6 13.722.875.72 12Williamson EntranceInletOutGnd NS 6.63 13Williamson OfficeInletOut1 NS 14Mat. SciencesStreetOutGnd NS 1 -11 12 -13 14 R6 R5 R1 333 mg PMEP 394 mg mc-PDMCH 1344 mg PMCH Low wind speed release The wind direction during the experiment on the 24 th changed throughout the morning from a forecast SE wind to an ENE wind, therefore the receptor points at the Simon building were not downwind of the pre-selected release points. Wind speed was below 4 m/s (> 1 m/s street level) during release. Tracers were released from ~1.7 km (PMCH), ~900 m mc-PDMCH) and ~400 m (PMEP) from the Simon Building. While most samples were not higher than background significant tracer concentration above background was found outside on the 6 th floor for all tracers, outside at the 4 th floor for PMCH and PMEP, and outside only for PMCH. These results could be explained by traffic, the A34 is a busy traffic route that was close to all release points with traffic moving NW and SE, however, tracer movement would be at street level and highest concentrations were not found at street level, but on the 6 th floor. Time series of tracer ingress 1 -11 Balcony Lab Aerosol Lab Computer Lab Six releases using one or three PFC tracers in different configurations and under different conditions were undertaken in Summer 2015. Background measurements were recorded periodically and averages taken, concentrations were considered significant if two standard deviations higher than background (Table 1). Three further experiments were conducted in the Autumn, to more closely investigate the rate of ingress and decay of tracer indoors. Results ChemicalMeanSD PMCH11.411.99 mc-PDMCH11.370.56 mt,pc-PDMCH7.310.45 PMEP5.580.79 PFD12.450.25 PFD22.280.32 Figure 7. Time series of tracer decay over 90 minutes for three rooms in the Simon Building; (a) the ‘aerosol lab’ a small mechanically-ventilated lab with closed windows, (b) the ‘balcony lab’ a small well ventilated lab with door open to outside and (c) the ‘computing lab’ a larger room used by students Tracer ReleasedDescriptionFloor2428 mg PMCH 474 mg mc-PDMCH 234 mg PMEP 2Gas CageStreetOutGnd 236.51NS2.81 5Simon Balcony LabRoomIn2 256.66NS 6Simon Balcony LabInletOut2 326.32NS 10Simon Computing LabRoomIn6 109.402.23NS 11Simon Computing LabInletOut6 329.58NS 12Williamson EntranceInletOutGnd 98.61NS143.10 14Mat. SciencesStreetOutGnd NS29.48NS 15Pivo CoffeeStreetOutGnd 14.81NS 17Swinton GroveParkOutGnd NS 18Ardwick GreenParkOutGnd NS 198.64 234 mg PMEP 474 mg Mc-PDMCH 2428 mg PMCH Dawn release Several experiments were conducted in the August campaign where one or more PFC tracers were released. The experiment presented here was undertaken at dawn (05:00 GMT) on the 23 rd July and exhibited the highest tracer concentrations after 2 km within the campaign. PMCH was released from ~ 2km away to the SW, while mc-PDMCH was released a similar distance to the WSW. PMEP was released closer to central Simon Building. High concentrations of tracer were found at all levels of the Simon Building, which may be due to a trapping of air at dawn [4]. Mc-PDMCH levels were not significant other than for the 6 th floor sample and the most northerly sampling point near the Materials Sciences Building, University of Manchester – where PMCH was not significantly above background. This shows a clear relation to wind direction in this experiment. Figure 5. Release points and sampling points for triple tracer release at 05:00 GMT, 23 rd July, in Manchester, UK. 1 -11 12 -13 15 14 17 18 R2 R3 R4 Table 3. Sampling positions and concentrations in ppq above background. NS denotes not significantly above background (a) (b) (c) Figure 6. Position of rooms in Simon Building. (b) (a) Table 1. Averaged background PFC concentrations Figures 2 and 3 are indicative of some of the measurements made in the August measurement campaign, indicating the variability of concentrations measured indoors and outdoors. Figure 2 shows that the highest concentrations occurred at dawn on 23 rd July, Figure 3 indicates that the second floor balcony lab has the greatest ingress of tracer. Figure 3. Ratio of PMCH measured indoors and outdoors when tracer level was significantly over background. Figure 2. Concentration of PMCH, released from ~2km away. measured outside the Simon building on ground, 2 nd, 4 th and 6 th floors PFC Tracers can vary considerably depending on location, height and time of day Highest tracer concentrations occurred at dawn – but requires further investigation Pollutants may persist within buildings having passed by outside At low wind speeds, tracer can be detected contrary to the prevailing wind direction. In an experiment in August, 1.3 g of PMCH was released 1.9 km away, average roof level wind speed was 7.8 m/s. The highest measurement of PMCH outside was 54 ppq above background, and 46 ppq inside. After the first 30 minutes, the PFC concentration returned to background levels outside, but other internal rooms still had elevated PFC concentrations between 10 and 16 ppq above background an hour after release. A follow up experiment was conducted on the 30th October; 10 minute samples were taken for 90 minutes in three rooms on the Simon building while tracer was released ~2 km away (PMCH), ~100 m away (mc-PDMCH) and from a room on the ground floor of the Simon Building (PMEP). Background levels were subtracted from the measured concentrations. Tracer from ~2 km can be seen in the well ventilated balcony lab, but quickly falls back to background. The Aerosol Lab has a longer decay, while the largest computing lab has least influx, but highest concentration of the internally released tracer. Figure 4. Release points and sampling points for triple tracer release at 13:30 GMT, 24 th July, in Manchester, UK. Table 2. Sampling positions and concentrations in ppq above background. NS denotes not significantly above background