“Particulate matter emissions generally are classified into two categories, PM and PM10. PM10 is a particulate matter with diameter less than 10 microns. All particulate matter can pose a health problem. However, the greatest concern is with PM10, because of its ability to bypass the body's natural filtering system. PM emissions are primarily dependent on the grade of fuel fired in the boiler. Generally, PM levels from natural gas are significantly lower than those of oils. Distillate oils result in much lower particulate emissions than residual oils. When burning heavy oils, particulate levels mainly depend on four fuel constituents: sulphur, ash, carbon residue, and asphatenes. These constituents exist in fuel oils, particularly residual oils, and have a major effect on particulate emissions. By knowing the fuel constituent levels, the particulate emissions for the oil can be estimated. Methods of particulate control vary for different types and sizes of boilers. For utility boilers, electrostatic precipitators, scrubbers, and baghouses are commonly utilized. For industrial and commercial boilers, the most effective method is to utilize clean fuels. The emission levels of particulate matter can be lowered by switching from a residual to distillate oil or by switching from distillate oil to a natural gas. Additionally, through proper burner set-up, adjustment and maintenance, particulate emissions can be minimized, but not to the extent accomplished by switching fuels”. Without great investments, particle emissions can be reduced of the following forms: Use fuel oils with low rates of nitrogen and sulphur. Optimise atomisation pressure of fuel oil. Good regulation of the relationship air/fuel oil. Appropriate burners maintenance. Knowing that there is a relationship of NOx emissions, with the contained nitrogen radicals in fuel, exists the possibility to mix fuel oil n. º 6 with fuel oil n. º 2 of low nitrogen in order to dilute the amount of nitrogen radicals, thus minimizing the emissions. Another form of emissions reduction is to use fuel additives to control fuel firing. Comments from the forum on the above subject would be appreciated. Thanks Luis Marques :)