BEIJING - Parts of China’s capital Beijing suffered air pollution more than 20 times recommended levels on Tuesday, but authorities refrained from issuing the highest smog alert. Counts of PM2.5 - harmful microscopic particles that penetrate deep into the lungs - reached 529, according to the US embassy, which issues independent readings. The World Health Organization’s recommended maximum exposure is 25 over a 24-hour period. China is often hit by heavy smog, mostly a result of coal burning. China’s state weather observatory issued a yellow alert - the second highest in a four-tier warning system - for smog in Beijing and other parts of north China, the official Xinhua news agency said.