An analyzer for measuring NH₃ emitted from a combustion process has been developed based on a simple non-dispersive infrared (NDIR) technique because of its cost-effective benefit. The weakness of the NDIR analyzer due to interference and zero-drift has been overcome. A least-interfering bandpass filter (BPF) was found and manufactured to compensate for the interfering effects of gases emitted from a combustion process (e.g., CO, NO_x, SO₂, CO₂, H₂O, HCl, formaldehyde, acetaldehyde and toluene). It was found that there was no significant interference in the least-interfering BPF with respect to gases of concern. Measurement errors by the analyzer were less than 2.5% in a range of 1 to 10 ppmv of NH₃ compared to a standard method when the compound was measured in complicated mixing gases. For the zero-drift, using BPFs with identical center wavelength with respect to different incident infrared intensity was found to help minimize the zero-drift of the NDIR analyzer. As a result, the analyzer could cut approximately 19% of zero-drift caused by the aging effect of both IR source and detector. It suggests that the analyzer could be applied for measuring NH₃ emitted from combustion processes with good accuracy and reproducibility.

A high humidity at a high temperature presents a common challenge in monitoring the air pollutants emitted from stationary sources. Thus, humidity removal is a pivotal issue. In this study, the effect of humidity pretreatment devices (HPDs) on hydrogen chloride (HCl) gas emitted from an incinerator stack was investigated. A conventional cooler (HPD_CL), and poly-tube (HPD_NP) and single-tube (HPD_NS) Nafion^™ dryers were used as HPDs in this study. HCl concentrations varied at five and 10 parts per million in volume (ppmv). Low (i.e., ~4%) and high (i.e., ~17%) humidities were generated at 180 °C. The removal efficiencies of humidity and the loss rates of HCl by the devices were determined. The removal efficiencies of humidity by HPD_CL and the two dryers were found to be similar, at approximately 85% at a low humidity and 95% at a high humidity. In terms of HCl loss rates, HPD_CL revealed the highest loss rates in all conditions (i.e., >95%), followed by HPD_NP and HPD_NS. At normal room temperature (i.e., 25 °C), the HCl loss rates of HPD_NP were >40% at a low humidity and >70% at a high humidity, while those of HPD_NS were >10% at a low humidity and >60% at a high humidity. The performance of the two dryers improved when they were heated to 80 °C. However, this temperature caused damage to the dryers, which reduced their lifetime.

A beta-ray attenuation monitor (BAM) is preferred as a reference instrument for monitoring particulate matter in the air due to its accuracy. However, BAM cannot be used in large numbers for spatial distribution monitoring because of its high investment cost. Thus, a mid-cost optical particle counter (OPC) is an alternative solution for widespread use. However, its long-term performance with respect to various monitoring environments should be taken into account. In this study, six mid-cost OPCs were used to measure PM_2.5 concentrations at an underground subway station and compared with a reference BAM over 15 months. OPCs were placed in the waiting space and platforms to compare PM_2.5 concentrations and determine PM_2.5/PM₁₀ ratios. The reference BAM was installed on the platform. Error analysis revealed a significant discrepancy, with normalized errors exceeding 30%, between the 1-h average PM_2.5 concentrations recorded by the BAM and OPCs at the same location. In contrast, the 24-h average PM_2.5 concentrations measured by the BAM and OPCs at the same location showed similar patterns, with stronger correlations (r² = 0.80–0.93) compared to the 1-h averages (r² = 0.63–0.83). The normalized errors for the 24-h averages ranged from 13.9% to 21.2%, depending on seasonal variations. These findings suggest that OPCs can effectively monitor 24-h average PM_2.5 concentrations in an underground subway station over a year without additional calibration, making them a cost-effective option. In addition, 1-h average PM_2.5 concentrations varied across different sampling spaces and were influenced by PM_2.5/PM₁₀ ratios. Hence, when measuring the 1-h average mass concentration of PM_2.5, it is essential to consider PM characteristics and seasons.

The zero drift, interference, and sensitivity of an HCl analyzer based on a non-dispersive infrared (NDIR) technique can be improved to develop a cost-effective solution for continuous emission monitoring systems (CEMSs). To achieve these improvements, the same bandpass filter technique, negligible interference bandpass filter, and optimal path length are applied to the analyzer. Laboratory inspections and long-term field trials are conducted to evaluate the performance of the analyzer. A metalworking factory and a cement factory are selected for field trials. In laboratory inspections, the relative error of the analyzer is less than 1%, aligning closely with the results obtained from standard ion chromatography methods. Moreover, the basic specifications of the proposed analyzer are comparable to those of commercial HCl analyzers. In field trials, the NDIR analyzer shows a significant bias compared to the standard method. However, when considering the difference between HCl emission levels and HCl emission standards, the relative errors are less than 10%. These results suggest the proposed NDIR analyzer is a practical option for the CEMS of metalworking and cement factories. However, seasonal variations should be considered when the temperatures of gas emissions are low.

Two prototype moss-based green roof systems were developed and evaluated using a newly cultivated strain of Racomitrium japonicum (Dozy & Molk.) to investigate their feasibility in mitigating rooftop heat and enhancing carbon sequestration under actual urban conditions. Flat and sloped-type green roof systems (2 m × 2 m each) were developed and installed on a rooftop to investigate their performance in summer (from June to August 2025). The moss-based systems reduced rooftop surface temperature by an average of 6–10 °C during daytime and retained approximately 1.5–2.5 °C of heat at night, thereby contributing to cooling and thermal buffering. The moss layer effectively reduced solar radiation heating of the underlying soil. Despite exposure to intense sunlight and high summer temperatures, the moss maintained a consistent growth rate of 3–5 mm per month. The annual carbon sequestration capacity of the prototype system was estimated at approximately 0.3 kg C/m².year, which is comparable to values reported for other vegetation types. These findings indicate that moss-based green roofs incorporating the newly cultivated moss strain have practical potential for urban heat island mitigation and carbon capture.