Photometrically measured continuous personal PM(2.5) exposure: levels and correlation to a gravimetric method

Low-Cost Sensor Node for Air Quality Monitoring: Field Tests and Validation of Particulate Matter Measurements

Air pollution is still a major public health issue, which makes monitoring air quality a necessity. Mobile, low-cost air quality measurement devices can potentially deliver more coherent data for a region or municipality than stationary measurement stations are capable of due to their improved spatial coverage. In this study, air quality measurements obtained during field tests of our low-cost air quality sensor node (sensor-box) are presented and compared to measurements from the regional air quality monitoring network. The sensor-box can acquire geo-tagged measurements of several important pollutants, as well as other environmental quantities such as light and sound. The field test consists of sensor-boxes mounted on utility vehicles operated by municipalities located in Central Switzerland. Validation is performed against a measurement station that is part of the air quality monitoring network of Central Switzerland. Often not discussed in similar studies, this study tests and discusses several data filtering methods for the removal of outliers and unfeasible values prior to further analysis. The results show a coherent measurement pattern during the field tests and good agreement to the reference station during the side-by-side validation test.

Exposure to fine particulate matter (PM2.5) from non-tobacco sources in homes within high-income countries: a systematic review

The health impacts associated with exposure to elevated concentrations of fine particulate matter (PM_2.5) are well recognised. There is a substantial number of studies characterising PM_2.5 concentrations outdoors, as well as in homes within low- and middle-income countries. In high-income countries (HICs), there is a sizeable literature on indoor PM_2.5 relating to smoking, but the evidence on exposure to PM_2.5 generated from non-tobacco sources in homes is sparse. This is especially relevant as people living in HICs spend the majority of their time at home, and in the northern hemisphere households often have low air exchange rates for energy efficiency. This review identified 49 studies that described indoor PM_2.5 concentrations generated from a variety of common household sources in real-life home settings in HICs. These included wood/solid fuel burning appliances, cooking, candles, incense, cleaning and humidifiers. The reported concentrations varied widely, both between sources and within groups of the same source. The burning of solid fuels was found to generate the highest indoor PM_2.5 concentrations. On occasion, other sources were also reported to be responsible for high PM_2.5 concentrations; however, this was only in a few select examples. This review also highlights the many inconsistencies in the ways data are collected and reported. The variable methods of measurement and reporting make comparison and interpretation of data difficult. There is a need for standardisation of methods and agreed contextual data to make household PM_2.5 data more useful in epidemiological studies and aid comparison of the impact of different interventions and policies.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11869-022-01288-8.

Influence of number of visitors and weather conditions on airborne particulate matter mass concentrations at the Plitvice Lakes National Park, Croatia during summer and autumn

We investigated the influence of local meteorological conditions and number of visitors on ambient particulate matter (PM) mass concentrations and particle fraction ratios at the Plitvice Lakes National Park between July and October 2018. Outdoor mass concentrations of particles with aerodynamic diameters of less than 1, 2.5, and 10 μm (PM₁, PM_2.5, and PM₁₀, respectively) and indoor PM₁ were measured with two light-scattering laser photometers set up near the largest and most visited Kozjak Lake. Our findings suggest that the particles mainly originated from background sources, although some came from local anthropogenic activities. More specifically, increases in both indoor and outdoor mass concentrations coincided with the increase in the number of visitors. Indoor PM₁ concentrations also increased with increase in outdoor air temperature, while outdoor PMs exhibited U-shaped dependence (i.e., concentrations increased only at higher outdoor air temperatures). This behaviour and the decrease in the PM₁/PM_2.5 ratio with higher temperatures suggests that the production and growth of particles is influenced by photochemical reactions. The obtained spectra also pointed to a daily but not to weekly periodicity of PM levels.

Characterizing peak exposure of secondhand smoke using a real-time PM2.5 monitor

Although short-duration elevated exposures (peak exposures) to pollutants may trigger adverse acute effects, epidemiological studies to understand their influence on different health effects are hampered by lack of methods for objectively identifying peaks. Secondhand smoke from cigarettes (SHS) in the residential environment can lead to peak exposures. The aim of this study was to explore whether peaks in continuous PM2.5 data can indicate SHS exposure. A total of 41 children (21 with and 20 without SHS exposure based on self-report) from 28 families in New York City (NY, USA) were recruited. Both personal and residential continuous PM2.5 monitoring were performed for five consecutive days using MicroPEM sensors (RTI International, USA). A threshold detection method based on cumulative distribution function was developed to identify peaks. When children were home, the mean accumulated peak area (APA) for peak exposures was 297 ± 325 hour*µg/m3 for children from smoking families and six times that of the APA from non-smoking families (~50 ± 54 hour*µg/m3 ). Average PM2.5 mass concentrations for SHS exposed and unexposed children were 24 ± 15 µg/m3 and 15 ± 9 µg/m3 , respectively. The average SHS exposure duration represents ~5% of total exposure time, but ~13% of children's total PM2.5 exposure dose, equivalent to an additional 2.6 µg/m3 per day. This study demonstrated the feasibility of peak analysis for quantifying SHS exposure. The developed method can be adopted more widely to support epidemiology studies on impacts of short-term exposures.

Variation in gravimetric correction factors for nephelometer-derived estimates of personal exposure to PM2.5

Many portable monitors for quantifying mass concentrations of particulate matter air pollution rely on aerosol light scattering as the measurement method; however, the relationship between scattered light (what is measured) and aerosol mass concentration (the metric of interest) is a complex function of the refractive index, size distribution, and shape of the particles. In this study, we compared 33-h personal PM_2.5 concentrations measured simultaneously using nephelometry (personal DataRAM pDR-1200) and gravimetric filter sampling for working adults (44 participants, 249 samples). Nephelometer- and filter-derived 33-h average PM_2.5 concentrations were correlated (Spearman's ρ = 0.77); however, the nephelometer-derived concentration was within 20% of the filter-derived concentration for only 13% of samples. The nephelometer/filter ratio, which is used to correct light-scattering measurements to a gravimetric sample, had a median value of 0.52 and varied by over a factor of three (10th percentile = 0.35, 90^th percentile = 1.1). When 33-h samples with >50% of 10-s average nephelometer readings below the nephelometer limit of detection were removed from the dataset during sensitivity analyses, the fraction of nephelometer-derived concentrations that were within 20% of the filter-derived concentration increased to 25%. We also evaluated how much the accuracy of nephelometer-derived concentrations improved after applying: (1) a median correction factor derived from a subset of 44 gravimetric samples, (2) participant-specific correction factors derived from one same from each subject, and (3) correction factors predicted using linear models based on other variables recorded during the study. Each approach independently increased the fraction of nephelometer-derived concentrations that were within 20% of the filter-derived concentration to approximately 45%. These results illustrate the challenges with using light scattering (without correction to a concurrent gravimetric sample) to estimate personal exposure to PM_2.5 mass among mobile adults exposed to low daily average concentrations (median = 8 μg m^-3 in this study).

Evaluation of Performance of Inexpensive Laser Based PM2.5 Sensor Monitors for Typical Indoor and Outdoor Hotspots of South Korea

Inexpensive (<$300) real-time particulate matter monitors (IRMs), using laser as a light source, have been introduced for use with a Wi-Fi function enabling networking with a smartphone. However, the information of measurement error of these inexpensive but convenient IRMs are still limited. Using ESCORTAIR (ESCORT, Seoul, Korea) and PurpleAir (PA) (PurpleAir U.S.A.), we evaluated the performance of these two devices compared with the U.S. Environmental Protection Agency (EPA) Federal Equivalent Monitoring (FEM) devices, that is, GRIMM180 (GRIMM Aerosol, Germany) for the indoor measurement of pork panfrying or secondhand tobacco smoking (SHS) and Beta-ray attenuation monitor (BAM) (MetOne, Grants Pass, OR) for outdoor measurement at the national particulate matter (PM2.5) monitoring site near an urban traffic hotspot in Daejeon, South Korea, respectively. The PM2.5 concentrations measured by ESCORTAIR and PA were strongly correlated to FEM (r = 0.97 and 0.97 from indoor pan frying; 0.92 and 0.86 from indoor SHS; 0.85 and 0.88 from outdoor urban traffic hotspot). The two IRMs showed that PM2.5 mass concentrations were increased with increased outdoor relative humidity (RH) levels. However, after applying correction factors for RH, the Median (Interquartile range) of difference compared to FEM was (14.5 (6.1~23.5) %) for PA and 16.3 (8.5–28.0) % for ESCORTAIR, supporting their usage in the home or near urban hotspots.

Impact of wood combustion for secondary heating and recreational purposes on particulate air pollution in a suburb in Finland

Little information is available on the concentrations of ambient fine particles (PM2.5) in residential areas where wood combustion is common for recreational purposes and secondary heating. Further, the validity of central site measurements of PM2.5 as a measure of exposure is unclear. Therefore, outdoor PM2.5 samples were repeatedly collected at a central site and home outdoor locations from a panel of 29 residents in a suburb in Kuopio, Finland. Source apportionment results from the central site were used to estimate the contributions from local sources, including wood combustion, to PM2.5 and absorption coefficient (ABS) at home outdoor locations. Correlations between the central and home outdoor concentrations of PM2.5, ABS, and their local components were analyzed for each home. At the central site, the average PM2.5 was 6.0 μg m(-)(3) during the heating season, and the contribution from wood combustion (16%) was higher than the contribution from exhaust emissions (12%). Central site measurements predicted poorly daily variation in PM2.5 from local sources. In conclusion, wood combustion significantly affects air quality also in areas where it is not the primary heating source. In epidemiological panel studies, central site measurements may not sufficiently capture daily variation in exposure to PM2.5 from local wood combustion.

Impact of personally measured pollutants on cardiac function

Epidemiological studies have shown associations between ambient air pollution and changes in heart rate variability (HRV). However, studies using personal air pollution measurements, especially with exposure averages <24h, are still rare. Between February and March 2008 HRV data as well as personal exposure to particulate matter <2.5μm (PM2.5), and particle number concentrations (PNC) were collected in five volunteers for up to 8.3h on a 5min resolution. Information about the participant's whereabouts was also collected. Mixed models were used to analyze concurrent and up to 30min delayed effects of air pollutants as well as being in traffic on 5min-averages of heart rate (HR), high and low frequency power (HF and LF), standard deviation of all normal-to-normal intervals (SDNN), and the root mean square of successive interval differences (RMSSD). Results are presented as %-change from the mean per increase in interquartile range of air pollutant. In total, 474 5-min segments were available for analysis. We observed concurrent and delayed reductions in SDNN of about 0.8-1.0% in association with a 5.4μg/m(3) increase in PM2.5. However, being in traffic by car led to an increase of about 20% 10-14min and 15-19min later. An increase in PM2.5 or PNC was associated with lagged decreases for RMSSD and HF. We detected concurrent reductions in RMSSD (-17.6% [95%-confidence interval: 29.1; -4.3]) when being in traffic by bike/foot. Being in traffic by car was associated with an immediate reduction in LF while more delayed increases in LF were observed when being in traffic by bike/foot. Air pollution and traffic effects on HR were less consistent. These rapid changes in HRV within 30min might be mediated by the autonomic nervous system in response to direct reflexes from receptors in the lungs.

Low-level exposure to ambient particulate matter is associated with systemic inflammation in ischemic heart disease patients

Short-term exposure to ambient air pollution is associated with increased cardiovascular mortality and morbidity. This adverse health effect is suggested to be mediated by inflammatory processes. The purpose of this study was to determine if low levels of particulate matter, typical for smaller cities, are associated with acute systemic inflammation. Fifty-two elderly individuals with ischemic heart disease were followed for six months with biweekly clinical visits in the city of Kotka, Finland. Blood samples were collected for the determination of inflammatory markers interleukin (IL)-1β, IL-6, IL-8, IL-12, interferon (IFN)γ, C-reactive protein (CRP), fibrinogen, myeloperoxidase and white blood cell count. Particle number concentration and fine particle (particles with aerodynamic diameters <2.5 μm (PM(2.5))) as well as thoracic particle (particles with aerodynamic diameters <10 μm (PM(10))) mass concentration were measured daily at a fixed outdoor measurement site. Light-absorbance of PM(2.5) filter samples, an indicator of combustion derived particles, was measured with a smoke-stain reflectometer. In addition, personal exposure to PM(2.5) was measured with portable photometers. During the study period, wildfires in Eastern Europe led to a 12-day air pollution episode, which was excluded from the main analyses. Average ambient PM(2.5) concentration was 8.7 μg/m(3). Of the studied pollutants, PM(2.5) and absorbance were most strongly associated with increased levels of inflammatory markers; most notably with C-reactive protein and IL-12 within a few days of exposure. There was also some evidence of an effect of particulate air pollution on fibrinogen and myeloperoxidase. The concentration of IL-12 was considerably (227%) higher during than before the forest fire episode. These findings show that even low levels of particulate air pollution from urban sources are associated with acute systemic inflammation. Also particles from wildfires may exhibit pro-inflammatory effects.

PM2.5 and CO concentrations inside an indoor go-kart facility

Three acute cardiovascular events within a 4-month period among drivers at an indoor go-kart arena prompted a visit to assess the magnitude of potentially hazardous air pollutant levels within the facility and help identify control measures. Carbon monoxide (CO) and particulate matter with aerodynamic diameters < 2.5 microm (PM2.5) were measured with personal, continuous-reading instruments to capture their spatial and temporal variability. Average driver and track CO levels during the sampling visit were comparable to state standards for worker exposures and exceeded some health-based guidelines. Average PM2.5 levels were low compared with regulatory standards, but transient PM2.5 peaks of unknown health impact were observed. Driver exposures were modestly but significantly higher than track concentrations measured by stationary monitors and substantially higher than outdoor concentrations. Driver exposures were partitioned into three components, attributed to (1) outdoor pollutants that were drawn unfiltered into the facility, (2) the persistent track cloud from previous races, and (3) proximity to the exhausts of other go-karts while driving in a race. Track cloud and tailpipe proximity components were the dominant contributors to driver CO exposure. The track cloud component lagged the number of go-karts on the track by 10-15 min. The dominant contributor to driver PM2.5 exposure was either the track cloud or outdoor component, depending on how many go-karts were racing simultaneously on the track. Transient spikes in PM2.5 were caused by proximity to other karts' tailpipes during passing events. Recommended methods for decreasing the track cloud component include modifying the ventilation system, race schedules, and number of go-karts racing simultaneously. The tailpipe proximity component can be reduced only by modifying go-kart exhausts or engines. This work represents a brief, limited sampling visit to a single facility, but it demonstrates the levels that are possible on a fairly high-usage afternoon. Future studies should be conducted to assess representative go-kart facility exposures at multiple facilities on multiple days.

Driver and passenger exposure to aerosol particles in buses and trams in Helsinki, Finland

This study investigates commuter and driver exposure to aerosol particles in buses and trams in Helsinki, Finland. Particle number and PM(2.5) concentrations were determined in the cabin and the driver's compartment. In addition, the <2.5 microm black carbon concentration was measured in the driver's compartment and PM(2.5) was collected for elemental analysis in the cabin. The measurements were repeated on two generations of buses and trams including two measurement days in each vehicle type. Fine particle number and mass concentrations in the driver's compartments were only slightly increased compared to Helsinki background air. Daily average ratios of number and mass to the background varied in range 0.8-4.3 and 1.0-2.9, respectively, both being the highest in the older bus type. However, the drivers were exposed to elevated levels of black carbon, which some studies have addressed to be strongly correlated with adverse health effects. The daily average ratio of black carbon to the background varied between 2.4 and 11.4. Additionally, the black carbon concentration had spatial variation. The drivers were exposed to higher peak concentrations of black carbon in downtown area. Particle concentrations were smaller in the driver's compartment than in the cabin. The newer technology in the newer model of the tram and bus seemed to decrease driver exposure to aerosol particles.

Determinants of personal and indoor PM2.5 and absorbance among elderly subjects with coronary heart disease

Epidemiological studies have established an association between outdoor levels of fine particles (PM2.5) and cardiovascular health. However, there is little information on the determinants of PM2.5 exposures among persons with cardiovascular disease, a potentially susceptible population group. Daily outdoor, indoor and personal PM2.5 and absorbance (proxy for elemental carbon) concentrations were measured among elderly subjects with cardiovascular disease in Amsterdam, the Netherlands, and Helsinki, Finland, during the winter and spring of 1998-1999 within the framework of the ULTRA study. There were 37 non-smoking subjects in Amsterdam and 47 in Helsinki. In Amsterdam, where there were enough exposure events for analyses, exposure to environmental tobacco smoke (ETS) indoors was a major source of between-subject variation in PM2.5 exposures, and a strong determinant of PM2.5 and absorbance exposures. When the days with ETS were excluded, within-subject variation accounted for 89% of the total variation in personal PM2.5 and 97% in absorbance in Amsterdam. The respective figures were 66% and 61% in Helsinki. In both cities, outdoor levels of PM2.5 and absorbance were major determinants of personal and indoor levels. Traffic was also an important determinant of absorbance: living near a major street increased exposure by 22%, and every hour spent in a motor vehicle by 13% in Amsterdam. The respective increases were 37% and 9% in Helsinki. Cooking was associated with increased levels of both absorbance and PM2.5. Our results demonstrate that by using questionnaires in connection with outdoor measurements, exposure estimation of PM2.5 and its combustion originating fraction can be improved among elderly persons with compromised health.

Field performance of a nephelometer in rural kitchens: effects of high humidity excursions and correlations to gravimetric analyses

Rural kitchens of solid-fuel burning households constitute the microenvironment responsible for the majority of human exposures to health-damaging air pollutants, particularly respirable particles and carbon monoxide. Portable nephelometers facilitate cheaper, more precise, time-resolved characterization of particles in rural homes than are attainable by gravitational methods alone. However, field performance of nephelometers must contend with aerosols that are highly variable in terms of chemical content, size, and relative humidity. Previous field validations of nephelometer performance in residential settings explore relatively low particle concentrations, with the vast majority of 24-h average gravitational PM2.5 concentrations falling below 40 microg/m3. We investigate relationships between 24-h gravitational particle measurements and nephelometric data logged by the personal DataRAM (pDR) in highly polluted rural Chinese kitchens, where gravitationally determined 24-h average respirable particle concentrations were as high as 700 microg/m3. We find that where relative humidity remained below 95%, nephelometric response was strongly linear despite complex mixtures of aerosols and variable ambient conditions. Where 95% relative humidity was exceeded for even a brief duration, nephelometrically determined 24-h mean particle concentrations were nonsystematically distorted relative to gravitational data, and neither concurrent relative humidity measurements nor use of robust statistical measures of central tendency offered means of correction. This nonsystematic distortion is particularly problematic for rural exposure assessment studies, which emphasize upper quantiles of time-resolved particle measurements within 24-h samples. Precise, accurate interpretation of nephelometrically resolved short-term particle concentrations requires calibration based on short-term gravitational sampling.

Evaluation and quality control of personal nephelometers in indoor, outdoor and personal environments

Personal nephelometers provide useful real-time measurements of airborne particulate matter (PM). Recent studies have applied this tool to assess personal exposures and related health effects. However, a thorough quality control (QC) procedure for data collected from such a device in a large-scale exposure assessment study is lacking. We have evaluated the performance of a personal nephelometer (personal DataRAM or pDR) in the field. We present here a series of post hoc QC procedures for improving the quality of the pDR data. The correlations and the ratios between the pDRs and the collocated gravimetric measurements were used as indices of the pDR data quality. The pDR was operated in four modes: passive (no pump), active (with personal sampling pumps), active with a heated inlet, and a humidistat. The pDRs were worn by 21 asthmatic children, placed at their residences indoors and outdoors, as well as at a central site. All fixed-site pDRs were collocated with Harvard Impactors for PM2.5 (HI2.5). By examining the differences between the time-weighted average concentrations calculated from the real-time pDRs' readings and recorded internally by the pDRs, we identified 9.1% of the pDRs' measurements suffered from negative drifts. By comparing the pDRs' daily base level with the HI2.5 measurements, we identified 5.7% of the pDRs' measurements suffered from positive drifts. High relative humidity (RH) affected outdoor pDR measurements, even when a heater was used. Results from a series of chamber experiments suggest that the heated air stream cooled significantly after leaving the heater and entering the pDR light-scattering chamber. An RH correction equation was applied to the pDR measurements to remove the RH effect. The final R2 values between the fixed-site pDRs and the collocated HI2.5 measurements ranged between 0.53 and 0.72. We concluded that with a carefully developed QC procedure, personal nephelometers can provide high-quality data for assessing PM exposures on subjects and at fixed locations. We also recommend that outdoor pDRs be operated in the active mode without a heater and that the RH effect be corrected with an RH correction equation.

Respirable particles and carcinogens in the air of delaware hospitality venues before and after a smoking ban

How do the concentrations of indoor air pollutants known to increase risk of respiratory disease, cancer, heart disease, and stroke change after a smoke-free workplace law? Real-time measurements were made of respirable particle (RSP) air pollution and particulate polycyclic aromatic hydrocarbons (PPAH), in a casino, six bars, and a pool hall before and after a smoking ban. Secondhand smoke contributed 90% to 95% of the RSP air pollution during smoking, and 85% to 95% of the carcinogenic PPAH, greatly exceeding levels of these contaminants encountered on major truck highways and polluted city streets. This air-quality survey demonstrates conclusively that the health of hospitality workers and patrons is endangered by tobacco smoke pollution. Smoke-free workplace laws eliminate that hazard and provide health protection impossible to achieve through ventilation or air cleaning.

Room chamber assessment of the pollutant emission properties of (nominally) low-emission unflued gas heaters

Pollutant emissions from unflued gas heaters were assessed in CSIRO's Room Dynamic Environmental Chamber. This paper describes the chamber assessment procedure and presents findings for major commercial heaters that are nominally "low-emission". The chamber was operated at controlled conditions of temperature, humidity, ventilation and air mixing, representative of those encountered in typical indoor environments. A fixed rate of heat removal from the chamber air ensured that the heaters operated at constant heating rates, typically approximately 6 MJ/h which simulated operation of a heater after warm-up in an insulated dwelling in south-east Australia. The pollutants assessed were nitrogen dioxide, carbon monoxide, formaldehyde, VOCs and respirable suspended particulates. One type of heater was lower emitting for nitrogen dioxide, but emitted greater amounts of carbon monoxide and formaldehyde (the latter becoming significant to indoor air quality). When operated with low line pressure or slight misalignment of the gas burner, this heater became a hazardous source of these pollutants. Emissions from the heaters changed little after continuous operation for up to 2 months.

PRACTICAL IMPLICATIONS

Unflued gas heaters have been popular as primary heating sources in Australian homes for many years due to their ease of installation and energy efficiency, with approximately 600,000 now installed in housing and schools. However, with concerns over potential health impacts to occupants, manufacturers have reduced the nitrogen dioxide emissions from unflued gas heaters in Australia over recent years. They have done so with a target level for nitrogen dioxide in indoor air of 300 p.p.b. This is somewhat higher than the ambient air (and WHO) guideline of 110 p.p.b. Several studies of child respiratory health show an impact of unflued gas combustion products. A full characterization of the combustion products is needed under conditions that simulate heater operation in practice-this study was undertaken to provide such characterization. Key findings are that the focus needs to be on total gas emissions (not just nitrogen dioxide), and that heater installation can be very sensitive to small faults which lead to very high levels of toxic pollutants. These findings have influenced current government proposals for emission limits for these heaters.