Relationships of outdoor and indoor ultrafine particles at residences downwind of a major international border crossing in Buffalo, NY

Fine and ultrafine particle removal efficiency of new residential HVAC filters

Particle air filters used in central residential forced-air systems are most commonly evaluated for their size-resolved removal efficiency for particles 0.3-10 µm using laboratory tests. Little information exists on the removal efficiency of commercially available residential filters for particles smaller than 0.3 µm or for integral measures of mass-based aerosol concentrations (eg, PM_2.5 ) or total number concentrations (eg, ultrafine particles, or UFPs) that are commonly used in regulatory monitoring and building measurements. Here, we measure the size-resolved removal efficiency of 50 new commercially available residential HVAC filters installed in a recirculating central air-handling unit in an unoccupied apartment unit using alternating upstream/downstream measurements with incense and NaCl as particle sources. Size-resolved removal efficiencies are then used to estimate integral measures of PM_2.5 and total UFP removal efficiency for the filters assuming they are challenged by 201 residential indoor particle size distributions (PSDs) gathered from the literature. Total UFP and PM_2.5 removal efficiencies generally increased with manufacturer-reported filter ratings and with filter thickness, albeit with numerous exceptions. PM_2.5 removal efficiencies were more influenced by the assumption for indoor PSD than total UFP removal efficiencies. Filters with the same ratings but from different manufacturers often had different removal efficiencies for PM_2.5 and total UFPs.

Monitoring of air pollution levels related to Charilaos Trikoupis Bridge

Charilaos Trikoupis bridge is the longest cable bridge in Europe that connects Western Greece with the rest of the country. In this study, six air pollution monitoring campaigns (including major regulated air pollutants) were carried out from 2013 to 2015 at both sides of the bridge, located in the urban areas of Rio and Antirrio respectively. Pollution data were statistically analyzed and air quality was characterized using US and European air quality indices. From the overall campaign, it was found that air pollution levels were below the respective regulatory thresholds, but once at the site of Antirrio (26.4 and 52.2μg/m³ for PM_2.5 and ΡΜ₁₀, respectively) during the 2nd winter period. Daily average PM₁₀ and PM_2.5 levels from two monitoring sites were well correlated to gaseous pollutant (CO, NO, NO₂, NO_x and SO₂) levels, meteorological parameters and factor scores from Positive Matrix Factorization during the 3-year period. Moreover, the elemental composition of PM₁₀ and PM_2.5 was used for source apportionment. That analysis revealed that major emission sources were sulfates, mineral dust, biomass burning, sea salt, traffic and shipping emissions for PM₁₀ and PM_2.5, for both Rio and Antirrio. Seasonal variation indicates that sulfates, mineral dust and traffic emissions increased during the warm season of the year, while biomass burning become the dominant during the cold season. Overall, the contribution of the Charilaos Trikoupis bridge to the vicinity air pollution is very low. This is the result of the relatively low daily traffic volume (~10,000 vehicles per day), the respective traffic fleet composition (~81% of the traffic fleet are private vehicles) and the speed limit (80km/h) which does not favor traffic emissions. In addition, the strong and frequent winds further contribute to the rapid dispersion of the emitted pollutants.

Effect of time-activity adjustment on exposure assessment for traffic-related ultrafine particles

Exposures to ultrafine particles (<100 nm, estimated as particle number concentration, PNC) differ from ambient concentrations because of the spatial and temporal variability of both PNC and people. Our goal was to evaluate the influence of time-activity adjustment on exposure assignment and associations with blood biomarkers for a near-highway population. A regression model based on mobile monitoring and spatial and temporal variables was used to generate hourly ambient residential PNC for a full year for a subset of participants (n=140) in the Community Assessment of Freeway Exposure and Health study. We modified the ambient estimates for each hour using personal estimates of hourly time spent in five micro-environments (inside home, outside home, at work, commuting, other) as well as particle infiltration. Time-activity adjusted (TAA)-PNC values differed from residential ambient annual average (RAA)-PNC, with lower exposures predicted for participants who spent more time away from home. Employment status and distance to highway had a differential effect on TAA-PNC. We found associations of RAA-PNC with high sensitivity C-reactive protein and Interleukin-6, although exposure-response functions were non-monotonic. TAA-PNC associations had larger effect estimates and linear exposure-response functions. Our findings suggest that time-activity adjustment improves exposure assessment for air pollutants that vary greatly in space and time.

Indoor and outdoor measurements of particle number concentration in near-highway homes

Exposure to high levels of traffic-generated particles may pose risks to human health; however, limited measurement has been conducted at homes near highways. The purpose of this study was to characterize differences between indoor and outdoor particle number concentration (PNC) in homes near to and distant from a highway and to identify factors that may affect infiltration. We monitored indoor and outdoor PNC (6-3000 nm) for 1-3 weeks at 18 homes located <1500 m from Interstate-93 (I-93) in Somerville, MA (USA). Median hourly indoor and outdoor PNC pooled over all homes were 5.2 × 10(3) and 5.9 × 10(3) particles/cm(3), respectively; the median ratio of indoor-to-outdoor PNC was 0.95 (5(th)/95th percentile: 0.42/1.75). Homes <100 m from I-93 (n=4) had higher indoor and outdoor PNC compared with homes >1000 m away (n=3). In regression models, a 10% increase in outdoor PNC was associated with an approximately equal (10.8%) increase in indoor PNC. Wind speed and direction, temperature, time of day and weekday were also associated with indoor PNC. Average mean indoor PNC was lower for homes with air conditioners compared with homes without air conditioning. These results may have significance for estimating indoor, personal exposures to traffic-related air pollution.

Indoor ultrafine particles of outdoor origin: importance of window opening area and fan operation condition

Inhalation exposure to ambient ultrafine particles (UFP) has been shown to induce adverse health effects such as respiratory and cardiovascular mortality. Human exposure to particles of outdoor origin often occurs indoors due to entry of UFP into buildings. The objective of the present study is to investigate entry of UFP into a building considering building operational characteristics and their size-dependent effects on UFP concentrations. Indoor and outdoor UFP concentrations along with air change rates were continuously measured in a full-scale test building. Estimates of infiltration factor, penetration coefficient, and deposition rate have been made for a range of particle sizes from 4 to 100 nm. The results show that UFP infiltration factor varies with particle diameter, window position, air change rate, and central fan operation. When the central fan was on continuously, the average infiltration factor ranged from 0.26 (particles <10 nm) to 0.82 (particles >90 nm) for two large window openings, and from 0.07 to 0.60 for two small window openings. Under the central fan-off condition, the average infiltration factor ranged from 0.25 (particles <10 nm) to 0.72 (particles >90 nm) for two small window openings, while it ranged from 0.01 to 0.48 with all windows closed. Larger window openings led to higher infiltration factors due to the larger extent of particle penetration into the building. The fan operation mode (on vs off) also has a strong impact, as the infiltration factor was consistently lower (up to 40%) when the fan was on due to additional particle deposition loss to the furnace filter and duct surfaces.

Penetration of ambient submicron particles into single-family residences and associations with building characteristics

This work improves knowledge of particle penetration into buildings by (i) refining a particle penetration test method that minimizes the duration and invasiveness required by individual tests without sacrificing accuracy, (ii) applying the method in an unoccupied manufactured test house and 18 single-family homes in Austin, Texas, USA, and (iii) exploring correlations between particle penetration and building characteristics, including results from blower door air leakage tests. The mean (± s.d.) measured penetration factor of submicron particles (20-1000 nm, not size-resolved) was 0.47 ± 0.15 in 19 residences that relied on infiltration for ventilation air, ranging from 0.17 ± 0.03 to 0.72 ± 0.08. Particle penetration factors (P) and outdoor particle source terms (P × air exchange rates) were both significantly and positively correlated with results from blower door air leakage tests. Outdoor particle source terms were also significantly and negatively correlated with the year of construction. These results suggest that occupants of leakier and older homes are exposed to higher indoor concentrations of outdoor submicron particles than those in tighter and newer homes, and that simple air leakage tests may be able to provide an approximate prediction of outdoor particle infiltration into single-family residences.

PRACTICAL IMPLICATIONS

Results from this work suggest that knowledge of simple building characteristics (i.e., the year of construction and blower door test results) may be used to predict the ability of outdoor particles to infiltrate into single-family residences, which could facilitate easier estimates of indoor exposures to outdoor particulate matter across the building stock. The methods within can also be extended to other buildings and can be used to assess possible changes in penetration factors because of envelope retrofits. Because outdoor particle size distributions were not measured during this study, these tests should also be repeated with size-resolved particle instrumentation.