The linking verb 是 shì (to be) is used with adjectives in the pattern—Noun + 是 + Adj + 的—to state or emphasize a fact or a perceived fact. For example: 他tā 是shì 男nán 的de。 He is male. 那nà 辆liàng 车chē 是shì 新xīn 的de　（那輛車是新的）。 That car is new. 那nà 只zhī 猫māo 是shì 黑hēi 的de（那隻貓是黑的）。 That cat is black.

This is not a easy question to answer. Beth's pattern is right, but you want to know when is it appropriate to use the pattern, don't you?

"那儿的空气品质不是很糟吗?" is said when someone else has done something which surprises the speaker because the thing contradicts the fact that 那儿的空气质量很糟。 e.g. "我们准备搬到北京去。“ "那儿的空气质量不是很糟吗?" It must be noted that when you say "那儿的空气质量不是很糟吗?"， the fact that 那儿的空气质量很糟 should be already known to the listener as well as yourself. Here's another example, in which 不是 is followed by a word that's not an adjective. "我昨天开车去了趟圣保罗。“ ”你不是不会开车吗？“

Off the top of my head, you can't say "Noun+是+adjective" independently, but it can be a clause coming after a main sentence. Examples: A：你认为他快乐吗？ B：我觉得他是快乐的。 Or, adding an intensive: 在我们班上，他是最高的一个同学。 Or, adding a measure word, 他是一个严肃的人。 Or, combining the above two forms, 她是一个很外向的小姑娘。

是 itself has various meanings, when it is a noun it is like 'be' 1.explaining or classifying: 他是男的。He is a man. 2. emphasizing the fact: 天气是冷。The weather is so cold.