ZEMCH 2019 International Conference Proceedings April.2020 | Page 283
household dust according to the sample as prepared(black), pink filter(red), water + pink filter (blue),
and RIL + pink filter(green); (f) Spectrum of reflected light of talc powder according to sample status
as: as prepared(black), water added(red), RIL added(blue), pink filter(green), water+pink filter(violet),
and RIL+ pink filter(brown)
Spectral sensor was used to characterize the light spectrum of samples under experimental
conditions. Figure 2‐e) and f) shows the spectrum of reflected light for household dust and talc powder
as a function of wavelength. Same measurement was performed under different conditions. Two
representative samples, household dust and talc powder were graphed and compared with peak
position in wavelength and peak intensity as well. In case of household dust, two peaks at 420 and
678nm in wavelength were observed. Under pink filter, the peak at 678 nm was observed to be removed
and peak shift from 420 to 440 nm was also observed. It is due to the light filtering at long wavelength
range by pink cellophane. Even though water and refractive index liquid are added, no significant shift
was observed. This results correspond with the measured chromaticity values well under additives.
Previously discussed chromaticity values in figure 1‐a) and b), overall values are centered to the white
region and relatively more shifts for blue, red, and yellow region were observed after refractive index
liquid was added. Meanwhile, talc powder revealed slightly different results with that of household
dust. Light spectrum for as prepared talc powder shows three peaks at 420, 677, and 720 nm,
respectively. No significant changes were observed for both additives cases, but combined condition of
pink filter and water addition, peak shift from 420 to 430 nm and additional peak is observed at 490
nm. Other peaks at long wavelength range were filtered same as before. For the comparison, similar
gypsum power was also characterized under pink filter and additives conditions. The peak at short
wavelength region shifted from 420 to 453nm, but no additional peak observed for talc case was not
detected. This results are correlated with the absolute amount of shift in chromaticity values is larger
for gypsum than that of talc powder.
4. Discussion
Chromaticity diagrams were constructed and light spectrum graph was drawn according to
different particulate matters under experimental conditions. Obvious change in chromaticity values
were observed for water and refractive index liquid were added cases. Depending on the intrinsic color
of samples, yellowish pollen and soil showed relatively shift to yellow region, and white powders such
as talc and gypsum moved to white centered region after adding water or refractive index liquid. From
the comparison with light spectrum. Noticeable relationship between shift in chromaticity values and
position in wavelength according to the type of sample under filter and additives. More distinct
dependency on filter color was observed for intrinsic white color powders such as talc and gypsum
rather than household dust, pollen and soil. Peaks at 420nm appears to be the guideline peak to
determine the influence of filter and additives depending on the type of sample. It was well agreed
with method called “browning index” in other color and light characterization method by using
spectrophotometer [8].
5. Conclusions
Color and light spectrum assisted optical sensing of particulate matters was operated in laboratory
scale and controlled experimental conditions. From the chromaticity values and reflected light
spectrum in terms of wavelength and intensity revealed the difference between samples according to
color and water or refractive index liquid additives. It was our observation that noticeable relationship
between chromaticity values and light spectrum depending on the type of particulate matter.
Appropriate combination of chromameter and spectral sensor can be an alternative approach to detect
particulate matters with higher selectivity.
Optical Sensing Assistance to Enhance Particulate Contaminants Detection
for Indoor Air Quality Monitoring
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