A researcher claims that the mean air concentration of nitrogen dioxide in U.S. cities is 9 parts per billion (ppb). In a random sample of 52 U.S. cities, the mean air concentration of nitrogen dioxide is 8.1 ppb. Assume the population standard deviation is 5.65 ppb. At α = 0.05, can you reject the claim?

(a) identify the claim and state H0 and Ha,

(b) find the standardized test statistic z,

(c) find the corresponding P-value,

(d) decide whether to reject or fail to reject the null hypothesis, and

(e) interpret the decision in the context of the original claim.