Indoor Pollen Concentrations of Mountain Cedar (Juniperus ashei) during Rainy Episodes in Austin, Texas

Abstract

Standard pollen monitoring programs evaluate outdoor pollen concentrations; however, information on indoor pollen is crucial for human wellbeing as people spend most of the day in indoor environments. In this study, we investigated the differences in indoor mountain cedar pollen loads between rooms of different uses and with different ventilation at The University of Texas in Austin and focused on the effect of rainy episodes on indoor/outdoor ratios of pollen concentrations. Pollen were sampled outdoors and indoors, specifically in seven rooms and in two thermal labs with controlled ventilation, during the daytime on 6 days in 2015. We calculated daily pollen concentrations, campaign pollen integrals (CPIn, the sum of all daily pollen concentrations) and ratios between indoor and outdoor concentrations (I/O ratio). Pollen concentrations differed substantially based on features related to room use and ventilation: Whereas the highest CPIn was observed in a room characterized by a frequently opened window and door, the smallest CPIn was related to a storeroom without any windows and no forced ventilation. Our results showed that rainy episodes were linked to a higher mean I/O ratio (0.98; non-rainy episodes: 0.05). This suggests that pollen accumulated indoors and reached higher levels than outdoors. Low ratios seem to signal a low level of risk for allergic people when staying inside. However, under very high outdoor pollen concentrations, small ratios can still be associated with high indoor pollen levels. In turn, high I/O ratios are not necessarily related to a (very) high indoor exposure. Therefore, I/O ratios should be considered along with pollen concentration values for a proper risk assessment. Exposure may be higher in indoor environments during prevailing precipitation events and at the end of the pollen season of a specific species. Standardized indoor environments (e.g., thermal labs) should be included in pollen monitoring programs.

Keywords: indoor pollen; mountain cedar; personal volumetric air samplers; thermal labs; ventilation.

Figure 1

Location of the study site in Texas, USA. (Data: North America political boundaries [32]; Land cover [33]).

Figure 2

Aerial picture of the West Mall Office Building on the University of Texas at Austin campus with thermal labs on the south of the building (© 2020 Google, CAPCOG); floor plan (fourth floor) with pollen measurement sites (modified after [34]).

Figure 3

(a) Juniperus pollen season in 2014/2015 in Austin, with dotted lines indicating the start and end dates of campaign 1 and campaign 2. Pollen data: KVUE and (b) corresponding precipitation and temperature data. Data: MesoWest.

Figure 4

Boxplots based on hourly pollen concentrations [pollen grains/m³] for (a) campaign 1 (20–23 January) and excl. site 10 (mean/median 749.4/64.0 pollen grains/m³) and (b) campaign 2 (3–4 February). The interquartile range is represented by the height of the boxes, the maximum and minimum values by the upper and lower whiskers and the median by bold horizontal lines in the boxes; points indicate outliers.

Figure 5

Boxplots showing ratios between hourly indoor and outdoor pollen concentration (I/O ratio) during campaign 1 (20–23 January) for nine sampling sites; grey = all data combined; dark grey = data sampled during rainy episodes (from 21 January 2 p.m. onwards); white = data sampled before the rainy episode; outliers not shown; I/O ratios >1 indicate more pollen indoors than outdoors. The interquartile range is represented by the height of the boxes, the maximum and minimum values by the upper and lower whiskers and the median by bold horizontal lines in the boxes.