In recent years, smog weather has appeared in many places in China, which has affected people's travel, work and health. Its formation is related to PM2.5, which refers to the atmosphere.

Analysis: (1) The sample data of a certain market are 32, 33, 34, 46, 62 and 69 respectively.

The sample data of city B are 34, 38, 5 1, 6 1, 63, 7 1 respectively.

. x A = 32+33+34+46+62+696 = 46，。 x B = 34+38+5 1+63+7 16 = 53；

Because. X A

So the air quality in a city is better.

(2) According to the stem and leaf chart, the air quality level of a city is Grade I in three days and Grade II in three days.

Three-day data of air quality level I are a 1, a2, a3, and three-day data of air quality level II are b 1, b2, b3.

Then all the cases of choosing two of the six days are: a 1a2, a 1a3, a 1b 1, a 1b2, a 1b3, a2b 1, and a2b/.

That is, the total number of basic events is15; ?

I still remember "One day the air quality level was Grade 1" as event A,

Then the basic events contained in event A are: a 1b 1, a 1b2, a 1b3, a2b 1, a2b2, a2b3, a3b 1, a3b2, a3b3,

That is, the number of events contained in event A is 9;

So p (a) = 9 15 = 35,

In other words, the probability that one day the air quality level is 1 level is 35.