Last night saw the poorest air quality (Very Unhealthy) for December 31 in Phoenix in 7 years. The forecast discussion at AIRNOW.gov says:
Forecast Discussion: A PM-2.5 HIGH POLLUTION ADVISORY IS IN EFFECT FOR TODAY JANUARY 01 PARTICLES: The worst air quality and highest fine particle (PM-2.5) levels for December 31 during the past seven years occurred yesterday. The combination of POOR dispersion, a strong (16 deg F) surface-based radiation inversion, a very shallow (1800) mixing depth, and mostly light or calm winds produced very stagnant conditions. As has been the case recently, despite High Pollution Advisory and Maricopa County No-Burn Day issuances, smoke from wood-burning activities caused PM-2.5 levels to spike during the overnight hours. The highest hourly concentration on Saturday was 322.2ug/m3 at the South Phoenix monitoring site at 11:00 p.m. Even higher readings occurred after midnight including 359.5ug/m3 at West Phoenix and 362.7ug/m3 at South Phoenix. Even though an increase in winds and dispersion will occur by this afternoon, the damage has already been done and another exceedance day will be the result. A strong to very strong ridge aloft is forecast to remain positioned over Arizona. Although stagnation of the local air mass due to warm air aloft and strong overnight inversion formation will continue in the Phoenix metro area as will the current dry spell an increase in down-slope winds is also expected Monday and Tuesday especially during the morning hours. Even though this will help with dispersion, elevated to high fine particle (PM-2.5) concentrations are expected to continue thru the forecast period.
The AQI Map (left) and the Phoenix area PM2.5 shows that the PM peaked overnight at midnight, right when the fireworks went off. There even was a report of a house fire in North Phoenix and the suspicion is a fireworks explosion. The 8 AM haze camera in Phoenix shows the lingering haze but by 1 pm this afternoon it has cleared markedly.
The Phoenix area has a nephelometer at the Estrella webcam site and the readings reached about 200 Mm-1 over night, increasing markedly at Midnight indicating that fireworks added to the air quality problem. To put this in perspective, this is as hazy as it was in Baltimore during the poor air quality days last July during the DISCOVER-AQ experiment. I checked on the AQ in Baltimore last night and neither DC or Baltimore (below right) had elevated PM during the fireworks displays last night.
California's central valley continues to suffer from stagnant air. On the left, I have posted the loop of streamflow for the last few days off the west coast and while you can see counter-clockwise circulation around lows which advect through the northwest, nothing is happening with the stagnant high (clockwise flow) which is stuck off the California coast. There is north-south flow just off the coast and then essentially nothing over land. The afternoon MODIS image shows the haze in the valley and the elevated AQI from Visalia south to Bakersfield. Below that I have pulled the AIRNOWTech PM readings in the valley which have been high all day. Hanford may have had a fireworks spike at Midnight.