Particle characterization in commercial buildings: A cross-sectional study in 40 offices in Singapore.

There is a knowledge gap in understanding how existing office buildings are protecting occupants from exposure to particles from both indoor and outdoor sources. We report a cross-sectional study involving weekly measurements of size-resolved indoor and outdoor particle concentrations in forty commercial building offices in Singapore. The outdoor and indoor particles size distributions were single mode with daytime peak number concentrations at 36.5 nm and 48.7 nm. Outdoor concentrations were significantly greater than indoors for all particle diameters. Indoor particle concentrations were generally low due to: 1) relatively high indoor particle removal (IPR) rates; 2) low indoor source strengths; and 3) low indoor particle of outdoor proportion (IPOP). We found that the ventilation system type had a substantial effect on indoor particle levels, IPR and IPOP. Through linear mixed model analyses, we identified dependencies of IPR rates with the use of MERV13 filters in supply air and filter maintenance frequency, IPOP with the use of MERV13 filters in the fresh air and supply air ducts and low particle source strength with regular daily cleaning presumably due to dust reservoir removal. Lastly, the contribution of outdoor sources was mainly seen for ultrafine and fine particles but less pronounced for coarse particles. This study provided detailed understanding of particle exposure in building offices and their influencing factors, facilitating future research on health impact of particle exposures.

Infiltration of fine particles in urban daycares.

Singapore is a tropical country with a high density of day-care facilities whose indoor environments may be adversely affected by outdoor fine particle (PM2.5 ) air pollution. To reduce this problem requires effective, evidence-based exposure-reduction strategies. Little information is available on the penetration of outdoor PM2.5 into day-care environments. Our study attempted to address the following objectives: to measure indoor infiltration factor (Finf ) of PM2.5 from outdoor PM2.5 and to determine the building parameters that modify the indoor PM2.5 . We collected indoor/outdoor 1-min PM2.5 from 50 day-care classrooms. We noted mean Finf  ± SD of 0.65 ± 0.22 in day-care rooms which are naturally ventilated and lower Finf  ± SD values of 0.47 ± 0.18 for those that are air-conditioned: values which are lower than those reported in Singapore residences. The air exchange rates were higher in naturally ventilated rooms (1.47 vs 0.86 h-1 ). However, fine particle deposition rates were lower for naturally ventilated rooms (0.67 ± 0.43 h-1 ) compared with air-conditioned ones (1.03 ± 0.55 h-1 ) presumably due to composite rates linked to the filters within the split unit air-conditioners, higher recirculation rates, and interior surfaces in the latter. Our findings indicate that children remaining indoor in daycares where air-conditioning is used can reduce their PM2.5 exposures during outdoor pollution episodes.

Home and day-care microenvironment exposure to Blomia tropicalis allergens and their associations with salivary eosinophilic cationic protein (ECP) among preschool children in Singapore.

To date, exposure studies linking dust-mite allergens with asthma and allergic morbidities have typically relied on sampling from representative locations in the home for exposure assessment. We determine the effects of differing microenvironments allergen exposures on asthma and asthma severity among 25 case and 31 control preschool children in Singapore. Blo t 5 allergen levels in various niches from the children's home and day-care microenvironments as well as their Blo t 5 time-weighted concentrations were determined. Eosinophilic cationic protein (ECP) levels from the children's saliva as markers for airway inflammation were obtained. Salivary ECP levels were higher in children with asthma than those without and the strength of association increased with higher salivary ECP levels. Although there was no relationship between time-weighted Blo t 5 concentrations with salivary ECP levels among the controls, a positive statistically significant relationship was noted among cases, demonstrating the effects of cumulative exposure on asthma severity. Avoidance measures to reduce Blo t 5 allergen exposure should include all microenvironments that asthmatic children are exposed throughout the day.

Impact of human presence on secondary organic aerosols derived from ozone-initiated chemistry in a simulated office environment.

Several studies have documented reductions in indoor ozone levels that occur as a consequence of its reactions with the exposed skin, hair and clothing of human occupants. One would anticipate that consumption of ozone via such reactions would impact co-occurring products derived from ozone's reactions with various indoor pollutants. The present study examines this possibility for secondary organic aerosols (SOA) derived from ozone-initiated chemistry with limonene, a commonly occurring indoor terpene. The experiments were conducted at realistic ozone and limonene concentrations in a 240 m(3) chamber configured to simulate a typical open office environment. During an experiment the chamber was either unoccupied or occupied with 18-20 workers. Ozone and particle levels were continuously monitored using a UV photometric ozone analyzer and a fast mobility particle sizer (FMPS), respectively. Under otherwise identical conditions, when workers were present in the simulated office the ozone concentrations were approximately two-thirds and the SOA mass concentrations were approximately one-half of those measured when the office was unoccupied. This was observed whether new or used filters were present in the air handling system. These results illustrate the importance of accounting for occupancy when estimating human exposure to pollutants in various indoor settings.

Estimates of associated outdoor particulate matter health risk and costs reductions from alternative building, ventilation and filtration scenarios.

Although many studies have reported calculations of outdoor particulate matter (PM) associated externalities using ambient data, there is little information on the role buildings, their ventilation and filtration play. This study provides the framework to evaluate the health risk and cost reduction of building, ventilation and filtration strategies from outdoor PM pollution on a nationwide level and applied it to a case study in Singapore. Combining Indoor Air Quality (IAQ) and time weighted exposure models, with established concentration-response functions and monetary valuation methods, mortality and morbidity effects of outdoor PM on the population of Singapore under different building, ventilation and filtration strategies were estimated. Different interventions were made to compare the effects from the current building conditions. The findings demonstrate that building protection effect reduced approximately half the attributable health cases amounting to US$17.7 billion due to PM pollution when compared to levels computed using outdoor data alone. For residential buildings, nationwide adoption of natural ventilation from current state is associated with 28% higher cases of mortality and 13 to 38% higher cases for different morbidities, amounting to US$6.7 billion. The incurred cost is negligible compared to energy costs of air-conditioning. However, nationwide adoption of closed residence and air-conditioning are associated with outcomes including fewer mortality (10 and 6% respectively), fewer morbidities (8 and 4% respectively) and economic savings of US$1.5 and 0.9 billion respectively. The related savings were about a factor of 9 the energy cost for air-conditioning. Nationwide adoption of mechanical ventilation and filtration from current natural ventilation in schools is associated with fewer asthma hospital admissions and exacerbations; although the economic impact is not substantial. Enhanced workplace filtration reduces the mortality and morbidity cases by 14 and 13% respectively amounting to savings of up to US$2.4 billion. The huge costs savings are comparable to the average worker salary and insignificant to energy, installation and rental cost. Despite uncertainty about accurate benefits, this study shows that health and economic gain via different building, ventilation and filtration designs in minimizing ingress of outdoor PM applied to a nationwide scale can be very large. Importantly, the results suggest that PM associated externalities and legislative efforts should not only focus on ambient PM reduction policies but also include building-informed decisions.