Flue gas analyzers are independently developed by Vasthi for domestic overseas environmental and industrial control site Monitoring online analysis. Based on DOAS and chemo metric algorithm, flue gas analyzer can measure SO2, NO, NO2, O2, NH3, CL2, O3, H2S etc., It can be widely used in environmental online monitoring, industrial process controlling, safety monitoring, etc.. Vasthi Flue gas analyzer applies UV DOAS technology .The optical technology consists of light sources, gas chamber, optical and spectroscopic and other optical components. flue gas analyzer has minimum detection limit of SO2, NO, NO2 can be 1mg/m(15m optical path). NO and No2 can be measured at the sametime, dispense with converter. and low detection limit. Flue gas analyzer has small amount of zero drift and span drift.It has Natural Gas Purification process.