SmogRank / Episodes / United States
Pennsylvania and Massachusetts, United States, January 2026
For 1 day, on 18 January 2026, 13 cities in the United States had PM2.5 at least twice their usual for the time of year. The worst reading was Newton, Massachusetts, United States: 34.3 µg/m³ on 18 January, about 6.9× its usual 3.4.
No cause named We have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached 13 in 1 country
Days 1 18 January 2026
Worst day 18 January 13 cities counted
Furthest above usual 6.9× Newton
Day by day
Play 18 January 13 cities at twice their usual or more
New City White Plains Newburgh Paterson Fort Lee Jersey City New York City Danbury Bayonne Elizabeth Linden Bridgeport New Brunswick Holbrook Waterbury New Haven Ewing Trenton Toms River Pittsfield Albany Bensalem Springfield North Chicopee Scranton Camden Sewell New London Atlantic City Pleasantville Chester Greenfield South Vineland Wilmington Utica Bear Newark Coventry Worcester Keene Elkton Dover Rutland Milford Providence Pawtucket Framingham Syracuse Fall River Edgewood Lowell Harrisburg Brockton Derry Boston Essex Quincy Hunt Valley Baltimore Lynn Haverhill Carlisle Laconia Scaggsville South Laurel Portsmouth Rockville Washington Oxon Hill-Glassmanor State College Rose Hill Springfield Hagerstown Ashburn Rochester Altoona Johnstown Buffalo St. Catharines Abington Philadelphia Pennsauken Lebanon Reading Norristown York Lancaster Allentown Bethlehem Hartford Lexington Newton 15 Jan 16 17 18 19 20 21 Every measured city in the area, coloured by its PM2.5 that day; a dark ring marks a city at twice its usual or more. Bars: cities counted each day, coloured by their median level. Choose a day or press play; without JavaScript, the days link to that day's world ranking.
How it spread
Newton Newton, 15 January: 8.6 µg/m³, 1.7× usual Newton, 16 January: no reading Newton, 17 January: 12.1 µg/m³, 2.4× usual Newton, 18 January: 34.3 µg/m³, 6.9× usual Newton, 19 January: 6.0 µg/m³, 1.2× usual Newton, 20 January: 2.6 µg/m³, 0.5× usual Newton, 21 January: 1.5 µg/m³, 0.3× usual Lexington Lexington, 15 January: 10.6 µg/m³, 2.1× usual Lexington, 16 January: 0.8 µg/m³, 0.2× usual Lexington, 17 January: 13.4 µg/m³, 2.7× usual Lexington, 18 January: 32.1 µg/m³, 6.4× usual Lexington, 19 January: 7.6 µg/m³, 1.5× usual Lexington, 20 January: 4.0 µg/m³, 0.8× usual Lexington, 21 January: 3.0 µg/m³, 0.6× usual Lancaster Lancaster, 15 January: 6.1 µg/m³, 0.7× usual Lancaster, 16 January: 5.7 µg/m³, 0.7× usual Lancaster, 17 January: 17.6 µg/m³, 2.1× usual Lancaster, 18 January: 30.7 µg/m³, 3.6× usual Lancaster, 19 January: 8.9 µg/m³, 1.0× usual Lancaster, 20 January: 5.5 µg/m³, 0.6× usual Lancaster, 21 January: 18.9 µg/m³, 2.2× usual York York, 15 January: 6.4 µg/m³, 0.8× usual York, 16 January: 7.3 µg/m³, 0.9× usual York, 17 January: 16.2 µg/m³, 1.9× usual York, 18 January: 29.3 µg/m³, 3.5× usual York, 19 January: 10.9 µg/m³, 1.3× usual York, 20 January: 6.4 µg/m³, 0.8× usual York, 21 January: 11.1 µg/m³, 1.3× usual Abington Abington, 15 January: 8.2 µg/m³, 0.6× usual Abington, 16 January: 8.2 µg/m³, 0.6× usual Abington, 17 January: 15.7 µg/m³, 1.1× usual Abington, 18 January: 29.3 µg/m³, 2.1× usual Abington, 19 January: 13.5 µg/m³, 1.0× usual Abington, 20 January: 7.9 µg/m³, 0.6× usual Abington, 21 January: 8.7 µg/m³, 0.6× usual Bethlehem Bethlehem, 15 January: no reading Bethlehem, 16 January: 5.1 µg/m³, 0.7× usual Bethlehem, 17 January: 17.7 µg/m³, 2.5× usual Bethlehem, 18 January: 28.4 µg/m³, 3.9× usual Bethlehem, 19 January: 7.7 µg/m³, 1.1× usual Bethlehem, 20 January: 5.8 µg/m³, 0.8× usual Bethlehem, 21 January: 11.2 µg/m³, 1.6× usual Lebanon Lebanon, 15 January: 6.1 µg/m³, 0.7× usual Lebanon, 16 January: 5.7 µg/m³, 0.7× usual Lebanon, 17 January: 22.1 µg/m³, 2.6× usual Lebanon, 18 January: 28.0 µg/m³, 3.3× usual Lebanon, 19 January: 9.4 µg/m³, 1.1× usual Lebanon, 20 January: 6.5 µg/m³, 0.8× usual Lebanon, 21 January: 13.2 µg/m³, 1.6× usual Reading Reading, 15 January: 6.3 µg/m³, 0.8× usual Reading, 16 January: 5.3 µg/m³, 0.7× usual Reading, 17 January: 16.5 µg/m³, 2.1× usual Reading, 18 January: 27.7 µg/m³, 3.5× usual Reading, 19 January: 8.4 µg/m³, 1.1× usual Reading, 20 January: 7.2 µg/m³, 0.9× usual Reading, 21 January: 13.1 µg/m³, 1.6× usual Norristown Norristown, 15 January: 6.3 µg/m³, 0.8× usual Norristown, 16 January: 4.8 µg/m³, 0.6× usual Norristown, 17 January: 14.5 µg/m³, 1.9× usual Norristown, 18 January: 26.3 µg/m³, 3.5× usual Norristown, 19 January: 9.0 µg/m³, 1.2× usual Norristown, 20 January: 6.2 µg/m³, 0.8× usual Norristown, 21 January: 10.0 µg/m³, 1.3× usual Allentown Allentown, 15 January: 6.7 µg/m³, 1.0× usual Allentown, 16 January: 5.0 µg/m³, 0.7× usual Allentown, 17 January: 17.2 µg/m³, 2.5× usual Allentown, 18 January: 26.2 µg/m³, 3.8× usual Allentown, 19 January: 8.0 µg/m³, 1.2× usual Allentown, 20 January: 5.5 µg/m³, 0.8× usual Allentown, 21 January: 10.5 µg/m³, 1.5× usual Hartford Hartford, 15 January: 10.8 µg/m³, 2.0× usual Hartford, 16 January: 3.6 µg/m³, 0.7× usual Hartford, 17 January: 15.4 µg/m³, 2.8× usual Hartford, 18 January: 26.0 µg/m³, 4.7× usual Hartford, 19 January: 9.5 µg/m³, 1.7× usual Hartford, 20 January: 6.7 µg/m³, 1.2× usual Hartford, 21 January: 8.8 µg/m³, 1.6× usual Pennsauken Pennsauken, 15 January: 7.7 µg/m³, 1.0× usual Pennsauken, 16 January: 5.1 µg/m³, 0.6× usual Pennsauken, 17 January: 12.0 µg/m³, 1.5× usual Pennsauken, 18 January: 26.0 µg/m³, 3.2× usual Pennsauken, 19 January: 9.3 µg/m³, 1.1× usual Pennsauken, 20 January: 7.1 µg/m³, 0.9× usual Pennsauken, 21 January: 7.1 µg/m³, 0.9× usual Philadelphia Philadelphia, 15 January: 7.4 µg/m³, 0.9× usual Philadelphia, 16 January: 6.0 µg/m³, 0.7× usual Philadelphia, 17 January: 13.0 µg/m³, 1.5× usual Philadelphia, 18 January: 25.5 µg/m³, 2.9× usual Philadelphia, 19 January: 10.0 µg/m³, 1.1× usual Philadelphia, 20 January: 6.0 µg/m³, 0.7× usual Philadelphia, 21 January: 7.8 µg/m³, 0.9× usual 15 Jan 16 17 18 19 20 21 Every counted city, in the order the episode reached them, 3 days before to 3 after. Each square is a day, coloured by that day's PM2.5; outlined: at twice the city's usual or more. Good 0–50
Moderate 51–100
Sensitive groups 101–150
Unhealthy 151–200
Very unhealthy 201–300
Hazardous 301+
Every city it reached
City Days Highest Usual Above usual
Newton Massachusetts, United States 1 18 January 3.4 6.9× Lexington Massachusetts, United States 1 18 January 4.4 6.4× Hartford Connecticut, United States 1 18 January 5.5 4.7× Bethlehem Pennsylvania, United States 1 18 January 7.2 3.9× Allentown Pennsylvania, United States 1 18 January 6.9 3.8× Lancaster Pennsylvania, United States 1 18 January 8.5 3.6× Norristown Pennsylvania, United States 1 18 January 7.5 3.5× York Pennsylvania, United States 1 18 January 8.4 3.5× Reading Pennsylvania, United States 1 18 January 8.0 3.5× Lebanon Pennsylvania, United States 1 18 January 8.5 3.3× Pennsauken New Jersey, United States 1 18 January 8.1 3.2× Philadelphia Pennsylvania, United States 1 18 January 8.7 2.9× Abington Pennsylvania, United States 1 18 January 13.7 2.1×
Daily means in µg/m³. Usual: the city's median for this time of year (its days within 21 days of the date, every year, leaving out the week around it). Above usual: its highest day against that.
Against other episodes in the United States
Number 60 of 98 episodes in the United States since our records began, by cities reached.
North-eastern United States and Canada, June and July 2023 279 North-eastern United States and Canada, July 2026 264 North-eastern United States and Canada, May and June 2023 260 North-eastern United States and Canada, July and August 2025 241 North-eastern United States and Canada, July 2023 241 North-eastern United States and Canada, June 2025 196 North-eastern United States and Canada, June 2023 161 North-eastern United States and Canada, July 2025 119 North-western United States and Canada, August 2023 110 North-eastern United States, June 2025 104 North-western United States and Canada, August 2026 99 North-eastern United States and Canada, February 2026 96 Pennsylvania and Massachusetts, United States, January 2026 13 Bars: cities reached; colour: the level of the episode's highest daily reading. All 98 .
Use this page SmogRank, Pennsylvania and Massachusetts, United States, January 2026: 13 cities with PM2.5 at twice their usual or more, 18 January 2026, smogrank.com/episodes/2026-01-pennsylvania-and-massachusetts-united-states (accessed 2 October 2026).
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You're welcome to reuse a single chart, image or figure with this citation and a link. Terms .
An episode is a run of days when many cities close to each other (four or more within 350 km on a day, 8 or more in all) each had a daily PM2.5 mean of at least 25 µg/m³ and at least 2 times their usual for that time of year. Found in our own measurements, not picked by hand. How we find episodes . Values are each city's daily mean of its own monitors; causes are the usual kinds for a pattern like this, not a confirmed source.
