Air pollution known as particulate matter 2.5 was measured at its highest levels this year, Tuesday, in Okinawa City where officials measured the level of particulates at 105 micrograms per cubic meter.

The monitoring of PM2.5 was started in 2011, and this was the fourth highest on the record.

Salt spray from the ocean is the overwhelmingly most common particulate source in the atmosphere, but sources also include motor vehicles and power plants. China, which uses massive amounts of coal and other fossil fuels, also influences Okinawa.

According to Okinawa Environmental Preservation Division, there’s no reason to worry. Officials explain that “The level of particulates rises at night and lowers during the day. But according to experts, even if the number rises to 100, it will not cause any health problems.”

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