Subject + 下降 + 了 + (Amount)
The verb 下降 (xiàjiàng) means "to decrease," "to decline," or "to drop" and describes a downward change in quantity, level, or value. It is commonly used with percentages and statistics. For example, 污染下降了 means "pollution decreased."
今年的销售额比去年下降了百分之十。
Jīnnián de xiāoshòu é bǐ qùnián xiàjiàng le bǎi fēn zhī shí.
This year's sales decreased by ten percent compared to last year.
气温突然下降,大家都穿上了厚外套。
Qìwēn tūrán xiàjiàng, dàjiā dōu chuān shàng le hòu wàitào.
The temperature dropped suddenly, and everyone put on thick coats.
近几年这个地区的犯罪率明显下降了。
Jìn jǐ nián zhège dìqū de fànzuì lǜ míngxiǎn xiàjiàng le.
The crime rate in this area has obviously decreased in recent years.