(46) For centuries the smoking of tobacco in cigarettes, cigars, and pipes has produced controversy over possible health hazards, but only since the 1950’s has sufficient scientific evidence accumulated to make possible a thorough evaluation of the health risk.
Scientific investigation of the relationship of smoking and health gained impetus after the beginning of the 20th century, then an increase in lung cancer was noted. As the use of tobacco increased, studies improved. (47) Although some gaps in knowledge still exist, the information now available is sufficient to permit making sound judgments, based on the converging lines of evidence.
(48) Investigators have directed their principal consideration to cigarette smoking because the health consequences attributed to it far exceed those due to smoking cigars and pipes. The widespread popularity of cigarettes is comparatively recent in man’s use of tobacco. The smoking pattern began to change at the beginning of the 20th century. Since then, cigarettes have steadily become more popular than cigars and pipes. (49) In the United States. per capita cigarette consumption — calculated for all persons 15 years of age and older, regardless of whether they smoked—rose from 49 per year in 1900 to 3,888 in 1960. Per capita consumption of cigars, pipe tobacco, and chewing tobacco declined sharply in the same period. Data presented in 1966 indicated a sharp reduction in cigarette smoking in the United States for men under the age of 55 with the trend continuing to 1970.
Further increase in cigarette consumption for women of all ages was reported in 1966 and no further increase was noted 1966 and 1970. However, in 1970 overall per capita cigarette consumption rose.
By 1962 the Royal College of Physicians of London reported:" Cigarette smoking is a cause of lung cancer and bronchitis, and various other less common diseases. It delays healing of gastric and duodenal ulcers." Some scientists, however, expressed dissenting opinions.
The most widely publicized report in the United States was issued in 1964 by the Surgeon General’s Advisory Committee on Smoking and Health. (50) The principal judgment in the committee’s 150,000-word report was: "Cigarette smoking is a health hazard of sufficient importance in the United States to warrant appropriate remedial action." The smokers of pipes and cigars were found to incur less health risk. However, the incidence of cancer and heart disease among them was found to be greater than among nonsmokers.
(49) In the United States. per capita cigarette consumption — calculated for all persons 15 years of age and older, regardless of whether they smoked—rose from 49 per year in 1900 to 3,888 in 1960.
2CO2 +N2。为了测定在某种催化剂作用下的反应速率，在某温度下用气体传感器测得不同时间的NO和CO浓度如表： 
