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Environmental and air monitoring research
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Abstract
Short-term exposures to indoor air contaminants can cause adverse health impacts and warrant a need for real-time measurements. The most common indoor pollutants are carbon dioxide (CO2), carbon monoxide (CO), ozone (O3), nitrogen dioxide (NO2), total volatile organic compounds (TVOCs), and particulate matter with a diameter of less than 2.5 μm (PM2.5). Several low-cost monitors for indoor air quality are commercially available; however, few of them are accurately tested. A stable, easy to use, and reproducible platform was developed in this paper.
In these laboratory conditions, the comparison between the low-cost sensors and calculated concentration was shown to be linear (R2 of 0.980, 0.972, 0.990, 0.958, 0.987, and 0.816 and rs of 0.982, 0.985, 0.900, 0.924, 0.982, and 0.571 for PM2.5, CO2, CO, NO2, TVOC (ethylene), and O3 respectively). Laboratory conditions were used to test possible cross-interferences to the TVOC sensor; an increase of CO2, CO, and NO2 of 2500 ppm, 100 ppb, and 100 ppb respectively generated a change in the curve fit from linear to quadratic. A complete validation of a low-cost sensor was achieved by its application in a real indoor place. Good correlation between the reference methods and uHoo measurements of PM2.5, CO2, and O3 was achieved (rs = 0.765 to 0.894, 0.721 to 0.863, and 0.523 to 0.622 respectively).
In a), precision of the measurements of PM of uHoo monitors. Readings of PM mass readings achieved using the uHoo monitors and the OPS are compared for different PM mass concentrations. Measurements were achieved using sodium chloride and each data point indicate one data set (minute-by-minute data), while the area behind the data point indicates the standard errors obtained by comparing the three different low-cost sensors used. Linearity of response and precision of measurements for the following gas sensors in uHoo monitors: CO2 b), CO c), NO2 d), and TVOC e). Propane is used as TVOC source. Theoretical calculations and uHoo monitors readings were compared. Each data point indicates one data set (minute-by-minute data), while the area behind the data point indicates the standard errors obtained by comparing the three different low-cost sensors used. In f), linearity of response and precision of measurements for the O3 sensor in uHoo monitors. An O3 meter was used as a reference. Each data point indicates one data set (minute-by-minute data), while the area behind the data point indicates the standard errors obtained by comparing the three different low-cost sensors used.
Reference
Baldelli, A. (2021). Evaluation of a low-cost multi-channel monitor for indoor air quality through a novel, low-cost and reproducible platform. Measurement: Sensors, 17. https://doi.org/10.1016/j.measen.2021.100059
Abstract
Comparison of ATP bioaerosol sampler and Andersen impactor using the aerosolized E.coli
In this study, a size-selective bioaerosol sampler was built and combined with adenosine triphosphate (ATP) bioluminescence assay for measuring the bioaerosol concentration more rapidly and easily. The ATP bioaerosol sampler consisted of a respirable cyclone, an impactor to collect bioaerosols onto the head of a swab used for ATP bioluminescence assay, a swab holder, and a sampling pump. The collection efficiency of the impactor was tested using aerosolized sodium chloride particles and then the particle diameter corresponding to the collection efficiency of 50% (cut-off diameter) was evaluated. The experimental cut-off diameter was 0.44 μm. The correlations between ATP bioluminescence (relative light unit; RLU) from commercially available swabs (UltraSnap and SuperSnap, Hygiena, LLC, U.S.A.) and colony forming unit (CFU) were examined using Escherichia coli (E. coli) suspension and then the conversion equations from RLU to CFU were obtained.
From the correlation results, the R2 values of UltraSnap and SuperSnap were 0.53 and 0.81, respectively. The conversion equations were the linear function and the slopes of UltraSnap and SuperSnap were 633.6 and 277.78, respectively. In the lab and field tests, the ATP bioaerosol sampler and a conventional Andersen impactor were tested and the results were compared. In the lab tests, concentrations of aerosolized E. coli collected using the sampler were highly correlated to those from the Anderson impactor (R2 = 0.85). In the field tests, the concentrations measured using the ATP bioaerosol sampler were higher than those from the Andersen impactor due to the limitations of the colony counting method. These findings confirm the feasibility of developing a sampler for rapid measurement of bioaerosol concentrations, offering a compact device for measuring exposure to bioaerosols, and an easy-to-use methodological concept for efficient air quality management.
Reference
Liao, L., Byeon, J. H., & Park, J. H. (2020). Development of a size-selective sampler combined with an adenosine triphosphate bioluminescence assay for the rapid measurement of bioaerosols. Environmental Research, 194, 110615. https://doi.org/10.1016/j.envres.2020.110615
Abstract
Chlorine-initiated oxidation of alkanes has been shown to rapidly form secondary organic aerosol (SOA) at higher yields than OH–alkane reactions. However, the effects of alkane volatile organic compound precursor structure and the reasons for the differences in SOA yield from OH–alkane reactions remain unclear. In this work, we investigated the effects of alkane molecular structure on oxidation by chlorine radical (Cl) and resulting formation of SOA through a series of laboratory chamber experiments, utilizing data from an iodide chemical ionization mass spectrometer and an aerosol chemical speciation monitor. Experiments were conducted with linear, branched, and branched cyclic C10 alkane precursors under different NOx and RH conditions.
Observed product fragmentation patterns during the oxidation of branched alkanes demonstrate the abstraction of primary hydrogens by Cl, confirming a key difference between OH- and Cl-initiated oxidation of alkanes and providing a possible explanation for higher SOA production from Cl-initiated oxidation. Low-NOx conditions led to higher SOA production. SOA formed from butylcyclohexane under low NOx conditions contained higher fractions of organic acids and lower volatility molecules that were less prone to oligomerization relative to decane SOA. Branched alkanes produced less SOA, and branched cycloalkanes produced more SOA than linear n-alkanes, consistent with past work on OH-initiated reactions. Overall, our work provides insights into the differences between Cl- and OH-initiated oxidation of alkanes of different structures and the potential significance of Cl as an atmospheric oxidant.
Reference
Jahn, L. G., Wang, D. S., Dhulipala, S. V., & Ruiz, L. H. (2021). Gas-phase chlorine radical oxidation of alkanes: effects of structural branching, NOx, and relative humidity observed during environmental chamber experiments. The Journal of Physical Chemistry A, 125(33), 7303–7317. https://doi.org/10.1021/acs.jpca.1c03516
Abstract
Atmospheric NO2 removal is urgent and necessary due to its negative effects on the eco-system. Here we developed the chrysanthemum flower-like silica (KCC-1) loaded with highly dispersed copper nanoparticles for efficient NO2 removal under ambient conditions. We carefully studied the NO2 removal performance of Cu-KCC-1 materials with different copper loadings (0, 5, 10, and 15 wt%) and demonstrated the Cu0 nanoparticles (10 wt%) boosted the NO2 removal capacity of KCC-1 by up to 51 times. KCC-1 loaded with 10 wt% of copper was verified to be the best-performing adsorbents, featuring an efficient NO2 removal capacity of 3.63 mmol/g and a moderate NO release (11.3%), which was primarily attributed to the presence of Cu0 nanoparticles.
The mechanistic study unveiled that the loaded Cu0 particles served as active adsorption sites for NO2 molecules and reduced the NO2 dissociation by covering the sites primarily responsible for NO2 dissociation (i.e., oxygen vacancies). This work affords a promising adsorbent for NO2 abatement under ambient conditions. The new knowledge established in developing adsorbents for NO2 would promote future research in this emerging and niche area of air pollution control.
Reference
Sun, M., Hanif, A., Wang, T., Yang, C., Tsang, D. C. W., & Shang, J. (2021). Chrysanthemum flower like silica with highly dispersed Cu nanoparticles as a high-performance NO2 adsorbent. Journal of Hazardous Materials, 418, 126400. https://doi.org/10.1016/j.jhazmat.2021.126400
Abstract
NO2 is a potent air pollutant because of its deleterious effects on human beings and other organisms. The state-of-the-art catalysis-based deNOx techniques (e.g., selective catalytic/non-catalytic reduction) are incapable of ambient NO2 abatement due to their low efficiency at temperatures below 300 °C. It is thus conceivable to directly capture NO2 from the atmosphere by selective adsorption on porous materials. This work reports the rational development and demonstration of the Mg–Al layered double hydroxides (LDHs) and their derived mixed metal oxides (MMO), using environmentally benign solvents, as high-capacity adsorbents for ambient NO2 abatement.
By boosting the densities of accessible basic sites using layer delamination strategies, the highest NO2 adsorption capacity of 8.52 mmol/g was achieved by the delaminated LDH material (LDH-AM), which was substantially higher than other popular and robust adsorbents, such as zeolites (0.36–3 mmol/g) and carbon-based adsorbents (2–6 mmol/g). Using Fourier transform infrared spectroscopy and powder X-ray diffraction, it was revealed that NO2 adsorption occurs on the surface M-OH basic sites and within the layers by simultaneously replacing the interlayer CO32− ions of LDH. This work affords not only promising, durable, and scalable adsorbents for ambient NO2 removal but also a strategy to develop adsorbents with high density of basic sites for capture of other pollutant acid gases from the environment.
Reference
Hanif, A., Sun, M., Wang, T., Shang, S., Tsang, D. C. W., & Shang, J. (2021). Ambient NO2 adsorption removal by Mg–Al layered double hydroxides and derived mixed metal oxides. Journal of Cleaner Production, 313, 127956. https://doi.org/10.1016/j.jclepro.2021.127956