Study On Key Detecting Technologies For Indoor Air Quality Controlling

At present,Indoor air quality(IAQ) problems have become the focal point of worldwide attention.It is an important prerequisite to detect indoor air pollutants for improving IAQ, which include formaldehyde(HCHO),benzene series,TVOC,radon gas,radiation,ammonia, et al.The detection of HCHO as the first pollutant is the most important.The main means of controlling IAQ is to install indoor air detection and purification unit on air-condition now. But bad odor from air-condition radiator aluminum plates will severely harm people health. Exact detecting and recognizing indoor HCHO and the odor from air-condition radiator aluminum plates in real time on the spot are two key detection technologies to control IAQ. The fabrication of material which is sensitive to HCHO,properties of HCHO sensor, electronic nose based on gas sensor array and BP neural network to recognize 0.06ppm HCHO in binary mixtures and system developed to detect the odor from air-condition radiator aluminum plates are systematically researched in the paper.SnO₂-NiO powders fabricated by chemical coprecipitation method belong to nanometer levels.The grain size of the powders changes in the range of 11 nm to 39nm according to the difference of NiO-doped concentration and the calcining temperature.Low concentration doped NiO greatly increases the quantity of adsorption oxygen and surface reactive sites.The reaction of HCHO gas and adsorbed oxygen speeds up to greatly improve the sensitive properties to HCHO gas.Low concentration doped NiO can effectively inhibit the growth of SnO₂ grains to decrease the grain size and increase specific surface area,which is beneficial to the oxygen adsorbing and the surface reaction between HCHO and adsorbed oxygen.The higher the calcining temperature of the powders,the larger the grain size.The SnO₂ peaks and no peaks of Ni species are observed in X-ray diffraction(XRD) pattern when NiO is doped at low concentration,because low concentration NiO is segregated on the surface of SnO₂.NiO peaks can be observed in XRD pattern of SnO₂-NiO powders calcined at 600℃at an atomic ratio of Sn:Ni=4:5 because the system takes place two-phase separation.The HCHO sensor is fabricated after annealing the MHP whose sensitive region the homogenized SnO₂-NiO powders are coated onto.The gas sensor characterization system is employed to test the HCHO sensor properties.The SnO₂-NiO HCHO sensor shows the electronic property behavior of n-type semiconductor.The HCHO sensor shows high response to low concentration HCHO,good stability and selectivity.The optimized working temperature is at 300℃and the power is about 180mW at 300℃.The response and recovery time change with the HCHO concentration.The environmental temperature has influence on the HCHO sensor and the relative humidity beyond 30%almost has no influence.The O₂ concentration in the atmosphere almost has no influence on the response to 0.06ppmHCHO and its interference gas.The quantitative recognizing of 0.06ppmHCHO and its interference gas in binary mixtures is realized by employing electronic nose technology based on the gas sensor array and back propagation(BP) neural network(NN).The gas sensor array is composed of above-mentioned HCHO sensor and several noble metal-doped SnO₂ thin-film sensors.The BP NN is constructed to recognize trace HCHO after the sensor array signals are compressed and reduced the dimensionality by PCA.The results show that the recognition rate to the single component HCHO is 88.8%and that to the HCHO in the presense of an interference gas,such as alcohol,toluene,α-pinene and VOCsmixture is 92%,89.3%,90.0%and 96.7%, respectively.The recognition rate is commensurable with that in literatures reported to recognize different kinds,different concentrations of gases by employing electronic nose. Electronic nose can effectively recognize 0.06ppmHCHO in binary mixtures.The odor detecting system is developed to aim at the odor from air-condition radiator aluminum plates.The system owns the repeatability and can detect in real time on the spot. The threshold value should be adjusted with the change of environmental temperature and humidity.The sensor array is composed of above-mentioned HCHO sensor and four commercial sensors.The sum of deltV data processing method combineds with NN is employed to process the sensor array signals.If |sum of deltV-threshold value| is bigger than 0.1,the sum of deltV data processing method can directly give the judgement to tested aluminum plates.If |sum of deltV-threshold value| is smaller than 0.1,the NN is used to further judge.The judgement results of the sum of deltV data processing method combineded with NN completely coincide with those of the odor specialist.The detection system has been used to detect the product quality in the production line by a internationally well-known Co.