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Informal economy i.e. unrecorded economy, is one of the important problems in developing countries which affects the efficiency of economic activities in formal sector. Informal economy is also an important source of air pollution. This paper aims at estimating informal economy in Iran over the period 1980-2009 based on the mount of CO2 emissions and the country forest areas and using Kalman Filter approach. The results indicate that: 1) there is a significant and long run relationship between CO2 emissions, the size of forest areas and firm’s industrial activities and total national product, 2) Total national product is more than recorded data in the study period so the existence of informal economy can’t be rejected during this period. 3) The average share of informal economy in total GDP is about 35.6 %.

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Due to the potentiality of the accumulation of atmospheric carbon dioxide and its permanent nature, the actual amount of carbon dioxide in the atmosphere, the accumulation of effective per capita carbon dioxide and the accumulation of effective per capita of this pollutant in the steady state has been estimated estimated through Kalman filter approach in a Ramsey equilibrium model over the period of 1991- 2007 for Iran. Thereby the researchers were able to estimate parameters such as the coefficient of environment cleaning for carbon dioxide, the share of fossil resources in production, the rate of time preference and the elasticity of emission function with respect to reduction activities.
   The empirical results of the study concerning the minimum, equilibrium & maximum rate of the coefficient of environment cleaning, indicate that for 1991 to 2007 in Iran the elasticity of fossil energy in production function is 0.4475, the rate of time preference is 0.12, the elasticity of emission function with respect to reduction activities is 4.45 and the coefficient of environment cleaning for carbon dioxide is 0.02. The effective per capita accumulated co2 & effective per capita accumulated co2 in steady state with the coefficient of seasonal cleaning of 0.02 respectively have the average of 50.45, 52.97 metric ton based on constant 2005 (PPP). Also the average of effective per capita consumption of the fossil fuel energy and the effective per capita capital in steady state are respectively 4.468 kg and 6.56  $ based on constant 2005 (PPP). The surpassing of the average value of the accumulation of carbon dioxide in steady state compared to its accumulation average value indicates that the accumulation path of co2 will have an increasing trend in next years.

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This paper tries to model the electricity demand in Iran’s industrial sector which captures economic factors and also non-economic exogenous factors. The structural time series model (STSM) approach is employed which allows using economic theory and time series flexibility. In this approach the role of UEDT (Underlying Energy Demand Trend) including technological improvement and structural changes is modeled, therefore the income and price elasticity are estimated more accurately. The results show that the UEDT has the stochastic nature. And UEDT has a great impact on industrial energy demand during 1975-2012. So, the electricity has not been used efficiently in this sector. In the short run the estimation of the income and price elasticity are 0.42 and 0.11 respectively. The value of the cross-price elasticity of electricity demand is estimated about 0.06. It shows that natural gas substitute electricity in industrial sector, however it is small.