Influencing the policy agenda has long been viewed as one of the most important sources of political power. For decades, scholars have maintained that the president has the most significant role in setting the policymaking agenda in Washington, but little systematic empirical work has been done to measure the president's influence. We explore the president's success in focusing the issue attention of Congress and the mass media by evaluating time-series measures of presidential, mass media, and congressional attention to five issues: crime, education, health care, U.S.–Soviet relations, and the Arab-Israeli conflict. We find that most of the time the president reacts, responding primarily to fluctuations in media attention and world events. In domestic policy, we find a more interactive relationship, one that appears to offer the president the opportunity to act in an entrepreneurial fashion to focus the attention of others in the system on major presidential initiatives.

No abstract

Laboratory characterizations of the peroxy radical chemical ionization mass spectrometer (PerCIMS) instrument have been performed. The instrument functions by drawing ambient air through a 50-microm-diameter orifice into an inlet held at low pressure. Peroxy radicals (HO2 and RO2) within this air are detected by amplified chemical conversion into a unique ion (HSO4-) via the chemistry initiated by the addition of NO and SO2 to the inlet. HSO4- ions are then quantified by a quadrupole filter mass spectrometer. PerCIMS provides measurements of the sum of peroxy radicals, HO2 + RO2 (HOxROx mode), or the HO2 component only (HO2 mode), achieved through the control of concentration of NO and SO2 added to the instrument. The characterization and response of this instrument have been evaluated through modeling of inlet chemistry and laboratory experiments and have also been demonstrated through successful deployment during field campaigns. The performance of PerCIMS with respect to calibration pressure and relative humidity is reported, as are the sensitivities of the instrument to organic peroxy radicals with different hydrocarbon groups. These data show PerCIMS to be a practical field instrument for the fast and accurate evaluation of the concentration of peroxy radicals over a variety of atmospheric conditions. The estimated accuracy of the derived [HOxROx] concentrations is +/- 35% (at the 95% confidence interval), while [HO2] measurements have accuracies of +/- 41% (at the 95% confidence interval). Typical precision of measurements well above the detection limit is 10%, and typical detection limits are 1 x 10(7) radicals cm(-3) for 15-s averaging times.