Correlations between gravimetry and light scattering photometry for atmospheric aerosols

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 PM 2.5 concentrations falling below 40 mg/m 3 . 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 mg/m 3 . 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.

Section: Scope Of This Papermentioning

confidence: 99%

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

Fischer¹,

Koshland²

2006

“…Nephelometers measure the particle light scattering extinction coefficient ( sp ) that can be related to particle mass concentration. Previous studies comparing nephelometer results to PM 2.5 impactor measurements indicate strong correlations ( 0.81< R 2 <0.96 ) when sampling kitchens fuelled with biomass in Mexico, in homes with wood stoves and ETS in rural British Columbia (Brauer, 1995;Brauer et al, 1996 ) and in ambient air (Waggoner and Weiss, 1980;Koenig et al, 1993;Thomas and Gebhart, 1994 ). In the present study, the performance of a nephelometer (Radiance Research Model M903, Seattle, WA ) for a large number of cooking and ETS sources was compared with mass concentrations determined using two different particulate mass concentration measurement techniques: a PM 2.5 Harvard Impactor (Marple et al, 1987 ) and a piezobalance (TSI Model 8510, St. Paul, MN ) equipped with a PM 3.5 impactor.…”

Section: Introductionmentioning

confidence: 98%

Assessment of indoor fine aerosol contributions from environmental tobacco smoke and cooking with a portable nephelometer

Bräuer

Hirtle

Lang

et al. 2000

Personal monitoring studies have indicated that environmental tobacco smoke ( ETS ) and cooking are major indoor particulate sources in residential and nonindustrial environments. Continuous monitoring of fine particles improves exposure assessment by characterizing the effect of time -varying indoor sources. We evaluated a portable nephelometer as a continuous monitor of indoor particulate levels. Simultaneous sampling with the nephelometer and PM 2.5 impactors was undertaken to determine the relationship between particle light scattering extinction coefficient ( sp ) and particle mass concentration in field and environmental chamber settings. Chamber studies evaluated nephelometer measurements of ETS and particles produced from toasting bread and frying foods. Field measurements were conducted in 20 restaurants and bars with different smoking restrictions, and in five residential kitchens. Additional measurements compared the nephelometer to a different mass measurement method, a piezobalance, in a well -characterized residence where various foods were cooked and ETS was produced. Since the piezobalance provides 2 -min average mass concentration measurements, these comparisons tested the ability of the nephelometer to measure transient particle concentration peaks and decay rate curves. We found that sp and particle mass were highly correlated ( R 2 values of 0.63 ± 0.98 ) over a large concentration range ( 5 ± 1600 g / m 3 ) and for different particle sources. Piezobalance and gravimetric comparisons with the nephelometer indicated similar sp vs. mass slopes ( 5.6 and 4.7 m 2 / g for piezobalance and gravimetric comparisons of ETS, respectively ) . Somewhat different sp vs. particle mass slopes ( 1.9 ± 5.6 m 2 / g ) were observed for the different particle sources, reflecting the influence of particle composition on light scattering. However, in similar indoor environments, the relationship between particle light scattering and mass concentration was consistent enough to use independent nephelometer measurements as estimates of short -term mass concentrations. A method to use nephelometer measurements to determine particulate source strengths is derived and an example application is described.

“…This temperature increment reduced the RH to below 50%, as estimated from a standard psychrometric chart (MIE, 1994); and (4) AH with a humidistat that switches on and off the electricity based on a pre-set RH level (AHH): This mode is the same as the AH mode except that the heater was set to be activated only when the ambient RH was over 85%. Although several studies (e.g., Thomas and Gebhart, 1994;Sioutas et al, 2000) observed the RH effect starting at 60%, our previous field tests (Quintana et al, 2000) showed that the RH effect on the pDR in the AUH mode was moderate between 60% and 85% and prominent above 85%. This, in conjunction with the concern of losing particle-bound semivolatile compounds due to heating the incoming air all the time (Bergin et al, 1997), prompted us to set the humidistat at 85%.…”

Section: Field Study Design and Instrumentsmentioning

confidence: 99%

“…Such devices need to be calibrated against gravimetric devices in the field, rather than relying on the calibration curve developed by the manufacturer with standard test dust. In addition, light-scattering is affected by relative humidity (RH) (McMurry and Stolzenburg, 1989;Thomas and Gebhart, 1994;Brauer, 1995;Day et al, 2000;Quintana et al, 2000;Day and Malm, 2001). Previous papers showed that the RH effect may be corrected by either physical (Sloane, 1984;Sloane and Wolff, 1985;Lowenthal et al, 1995;Sioutas et al, 2000) or statistical models (Richards et al, 1999), or prevented by using a heater (Liu et al, 2002) or a diffusion drier (Sioutas et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

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

Delfino

Floro

et al. 2004

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 PM 2.5 (HI 2.5 ). 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 HI 2.5 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 lightscattering chamber. An RH correction equation was applied to the pDR measurements to remove the RH effect. The final R 2 values between the fixedsite pDRs and the collocated HI 2.5 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.