A system and method for monitoring environment employ a dense network of low-cost sensor nodes. The method includes obtaining environmental information by combining a plurality of observations; wherein the plurality of observations are made with in-situ or remote sensors; wherein the sensors are of different degrees of accuracy in a way to complement each other, and of different cost, and wherein the low-cost sensors form a high-density network comprising a plurality of distributed sensors. The system can monitor gas concentrations over urban areas, industrial, forest, farm, wetland, power plants and other types of surfaces.
