In modern times, fireworks refer to fireworks and firecrackers set off in celebration ceremonies, but in ancient times, the usage of fireworks is not just fireworks made of gunpowder, but also has more meanings. Using fireworks to describe Yangzhou in March, of course, does not mean setting off fireworks to celebrate.
There is a view that the fireworks here probably refer to the smog in the south of the Yangtze River in spring, but it has not been recognized by scholars. Most scholars think that fireworks refer to catkins. Because willows are generally planted in the south, a lot of catkins will fall in spring, which is very artistic for poets. We will often see the shadow of catkins in the poet's spring scenery. Fireworks are rarely used to describe fog.
Fireworks Liuxiang is also a common usage of fireworks, but here fireworks refer to singers and dancers, while fireworks Liuxiang refers to brothels. In some poets' poems, fireworks and flowers are often used to refer to these singers and dancers. Perhaps in the eyes of poets, these singers and dancers are as beautiful as catkins.
Generally speaking, compared with modern fireworks, ancient fireworks have more usages and richer meanings. But the meanings of words in poetry often need to be understood in context. If there is no context, you might think that the poet wrote about Yangzhou, where fireworks were set off in mid-March, or the fireworks Liuxiang, which went to Yangzhou in March. These explanations are different from the intention expressed by the poet, and also affect the interpretation of the poem.