San Francisco, Oct 30 (IANS): US-based investment bank Morgan Stanley analysts tracking the air quality in China claimed that the production of iPhones has historically led to a reduction in air quality in four key Chinese cities -- Zhengzhou, Shenzhen, Chengdu and Chongqing.

In the city of Shenzhen, Morgan Stanley believes industrial production first spiked in early September, but remained below its usual levels for the same time last year, reports MacRumors.

In Chengdu, the analysts found that industrial activity has increased in recent days.

Likewise, in Chongqing, industrial production has ramped significantly higher in recent days, after an initial uptick and pullback in September.

"As of October 26, air quality data from Zhengzhou, also known as 'iPhone City', shows that industrial production levels have spiked higher recently, about a month later than historical seasonality, which we believe coincides with the ramp in iPhone 12 mass production," the analysts wrote.

According to analysts, they have seen an increase in nitrogen dioxide levels in the air. This pollutant is a direct cause of increased industrial production, it says. The nitrogen oxide causes acid rains, decreases the yield of crops, and more importantly, causes human health issues.

Taiwanese carriers have forecast that Apples latest iPhone 12 series will have stronger sales than the iPhone 6 and iPhone 6 Plus.

Apple suppliers Foxconn and Pegatron are offering workers on the assembly line increased bonuses in order to keep up with the strong demand for devices, following pre-orders for the iPhone 12 and iPhone 12 Pro.