This paper presents a novel sensor array based on MEMS-technology for quantitative measurement of the air quality and a novel model based measurement strategy. The sensor array consists of SnO2 - gas sensors, a porous silicon based humidity sensor and a Pt-temperature sensor monolithically integrated on a single chip. It was fabricated using SOI-technology, Pt-metallization and bulk micromachining. Good characteristics of the sensor array in terms of thermal properties, sensitivity, selectivity and time response have been achieved. The values of gas content and atmospheric humidity evaluated based on the developed sensor models are in a good consistence with the actual values.