Various techniques to measure SO2 concentration based on Differential Optical Absorption Spectroscopy (DOAS) have been widely developed and applied for various measurements. However, most of the applications are still relatively expensive. Some efforts have been made to reduce the cost by using Ultraviolet Light Emitting Diodes (LEDs) as light sources, showing promising results. Further reductions can be possibly made by providing an alternative to replace high spectral resolution spectrometers widely used in DOAS applications since those spectrometers are commercially expensive. This paper studies the feasibility of a DOAS instrument using a low-cost spectrometer and UV-LEDs as light sources. The resolution of the spectrometer is 0.7 nm. With this resolution, it is expected that the instrument hardly captures narrow band structures of SO2 optical absorption in the spectral range between 280 nm and 320 nm when measuring SO2 gas concentration lower than the limits of SO2 emissions regulated by the Indonesian government. To compensate for this drawback, narrow and broad bands of optical absorption structures are considered in the data analysis to achieve a detection limit far below the regulated limits. To capture the broadband structures, four UV-LEDs are used to cover spectral absorption from 250 nm to 320 nm. The instrument was calibrated using eight different standard concentrations of SO2. The correlation between the readings and the standard concentrations is high, indicated by the Pearson correlation coefficient of 0.9999. It was also found that the lowest concentration the instrument can distinguish from blank samples or the Limit of Detection is 16 ppm. However, the instrument can precisely measure concentrations higher than or equal to 25 ppm with a standard deviation of less than 10% of the mean concentration measured from five measurements. This is far below the required legal limits, below 229 ppm. After the calibration, the DOAS instrument was used to measure SO2 sampled from the emission of burning coals. To compare, a commercial SO2 sensor was used to measure the same gas. The results indicate that the difference in the readings between the two instruments is around 6% of the concentration.

Crumb rubber is one of Indonesia’s agroindustry export commodities. This industry faces environmental problems due to their wastes, both liquid and air. The source of air pollution is commonly from drying process that emitted odor from its evaporation and heating phenomena. Industry uses wet scrubber technology as air pollution control from emitted odor from drying process. Preliminary identification in noncontrolled wet scrubber shown that wet scrubber efficiency around 47%. Low efficiency wet scrubbing process causes rain drop of water vapor around drying process. This research used electrochemical based sensor MICS 5524 as ammonia monitoring instrument, assisted with arduino as microcontroller to regulate water discharge through valve controlling scrubbing process. This electrochemical based sensor reads ammonia based on voltage reads by Arduino microcontroller. Ammonia reading then control scrubbing process by adjusting valve opening for spray water distribution. Wet scrubber efficiency increases to 66,96% due to water scrubbing control, also can save water utilization as high as 61,90%, followed by absence of rain drop contains ammonia around drying process area.

The coal used as a primary fuel in an Indonesian power plant produces sulfur dioxide emission from its burning process. Several testing and monitoring methods developed, from laboratory analysis, CEMs based instrument, and absorption spectroscopy method developed for this purpose. Differential Optical Absorption Spectroscopy (DOAS) method based on Lambert-Beer law used as emission quantification. DOAS instrumentation developed in this research to measure sulfur dioxide as one of the emission parameters. Sulfur dioxide generated from the reaction between the sulfuric acid and dilute sodium sulfite. CCD spectrometer used to measure sulfur dioxide spectrum intensity at 260 to 350 nm absorption cross-section. There is a high correlation between sulfur dioxide gas produced by that reaction to spectrum intensity, with coefficient determination (r2) 0.9783, 0.9822, 0.9866, 0.9928 or coefficient correlation (r) 0.989, 0.991, 0.993, and 0.996 from lowest range concentration to highest range concentration. Precision analysis from gas calibration standard using Horwitz ratio indicates instrument setup precise enough with 0.504 Horwitz ratio, according to its acceptable range. The suspended particulate matter may interfere with UV penetration into CCD detector in emission simulation test using gasoline generator exhaust that causes 2.5 times deviation error between typical 800 ppm concentrated sulfur dioxide from chemical reaction and gasoline generator exhaust.

This research report new method for ammonia gas concentration measurement using metal oxide sensor-based instrument. Ammonia gas prepared by diluting concentrated liquid ammonia in water collected in container. Ammonia gas then streamed into monitoring path made by acrylic cube. Ammonia gas concentration measured as voltage from MEMS MICS 5524 sensor, then with ESP 8266 based iOT module logged into google sheet. Correlation between voltage and ammonia gas concentration evaluated by linearity test, compare with SNI 19-7117.6-2005 standard method and resulted more than 0,9 liniearity. This measurement totally nondestructive test, it carries no chemical agent could damage environment.

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