US Pacific north-west blanketed in thick smoke as firefighters push back blazes

Wildfires raging in the US Pacific North-west are blanketing the region with thick smoke, delivering some of the world’s worst air quality even as firefighters made progress against larger blazes in Washington state.As of Thursday afternoon, Seattle, Washington, and Portland, Oregon, hovered at the top of Swiss company IQAir’s list ranking the most polluted cities globally.In the two metropolises, air quality sensors showed readings above 100 in some locations, which is considered unhealthy for sensitive groups such as people with heart or respiratory conditions.In portions of central and eastern Washington and Oregon, sensors detected air quality indexes reaching above 200, which is categorized as “very unhealthy”.In the Seattle area, the smoke is forecasted to clear up by Friday, according to the Washington-department-of-ecology" class="entity-link entity-organization" data-entity-id="180096" data-entity-type="organization">Washington department of ecology, but poor air quality may persist to the east in Spokane. An air quality advisory issued by Oregon officials for the Portland area is expected to lift on Thursday evening.Meanwhile in Washington, firefighters have taken advantage of cooler weather to begin getting a handle on blazes that have displaced tens of thousands of people around the state’s second-largest city, but hotter, drier and breezier days lie ahead.Officials reported on Wednesday that firefighters had established containment lines around the perimeters of all three fires affecting Spokane and that they were focused on reinforcing those lines. Temperatures were expected to climb from 80F the past two days into the upper 90F (36C), with less humidity, late this week.The fires – one of which authorities say was deliberately set by a man who was arrested and charged with arson – have destroyed about 850 buildings and forced the evacuation of about 67,000 people since they erupted last weekend. Damage assessment crews have yet to tally exactly how many houses have been lost or damaged. No deaths have been reported.The other two fires were also started by people, though not necessarily deliberately, investigators have said. They remain under investigation. Those fires, the Autumn Lane and Fairview fires, started independently of the arson-caused Old Trails fire, they said.John Nowels, the Spokane county’s sheriff, said during a Wednesday news conference that the evacuation zones will remain in place due to incoming weather and fire danger.“We are not going to be downgrading these zones in any large way for many, many more days to come,” he said. “If we let people back in and we don’t have a high degree of certainty the fire lines will hold, we will put people in danger.”Many evacuees remained in a shelter set up in a Spokane convention center, at hotels or rentals, or at the homes of friends or relatives, with no idea of how soon they might go back – if they have a house to return to.The fires were among dozens across the western US that have stretched the ability of federal, state and local agencies to fight them.In Washington, there are 16 uncontained wildfires burning more than 672 sq miles (1,740 sq km) and being fought by more than 7,000 fire personnel, said Thomas Kyle-Milward, a spokesperson for the Washington department of natural resources.“We’re looking down the barrel at one of the worst fire seasons in state history,” he said.The man charged with starting the Old Trails fire, Aaron F Farinacci, 37, of Spokane, was expected to be arraigned on Thursday. According to court documents, he was arrested after a resident reported him being in the area where the fire began. He denied having started it when questioned by deputies.Authorities said they previously contacted him during two fire investigations last year, including one in a state park that prompted evacuation notices, though he was not charged in either.In California, authorities said on Wednesday that they arrested a 65-year-old man on suspicion of sparking a major wildfire by recklessly operating equipment without complying with state fire prevention requirements. Prosecutors will determine whether to file criminal charges. The blaze that erupted on Monday had scorched nearly 15 sq miles (39 sq km) of forest in Calaveras county, south-east of Sacramento.Associated Press contributed reporting