Bacon and eggs, candles and incense, break pads and so much more…


Air quality standards classify particles according to their size. Particles with a diameter of 10 microns or smaller (PM 10) have the potential to be inhaled into the lungs, posing potential health risks. Another category of concern is fine particulate matter, known as particles with a diameter of 2.5 microns or smaller (PM2.5), which also poses a threat to respiratory health.

You may have seen many articles about wood-burning stoves and particulate matter (PM2.5 and PM10). However, what you probably haven’t researched is that the main causes of PM2.5 lay elsewhere, either natural or industrial – and some of them are very surprising.


Some surprising culprits


One of the main indoor pollution sources for PM2.5 is cooking especially when certain cooking methods are employed.  Frying, grilling, and broiling can produce higher levels of particulate matter compared to methods like boiling or steaming. The combustion of cooking oil and fats, especially at high temperatures, can release particles into the air.

For example, gas stoves can produce combustion by-products, including fine particles. Electric stoves, while not completely emission-free, generally produce fewer particles compared to gas stoves. Cooking at higher temperatures increases the PM2.5 levels (i.e. eggs in a frying pan, or oven cooking poultry over a prolonged period.

In a research study, it was found that indoor PM2.5 concentrations in the house reached 200 micrograms per cubic meter for one hour during the cooking day. This exceeded the average of 143 micrograms per cubic meter observed in Delhi, the sixth most polluted city globally, and was significantly higher than the central London average of 15 micrograms per cubic meter. 

According to the US air quality index, a measure of city pollution, indoor air quality ranged from “unhealthy” to “very unhealthy” for almost two hours. These levels surpassed the World Health Organization’s guidelines of 10 micrograms per cubic meter for eight and a half hours. 

The simple act of cooking bacon and eggs can drastically increase PM2.5 particles in the indoor air. And even the seemingly harmless activity of toasting bread increased PM2.5 levels to 30 micrograms per cubic meter.


Air fresheners can contribute to the indoor concentration of particulate matter, including PM2.5. These products often contain volatile organic compounds (VOCs) and other chemicals that can be released into the air when the air freshener is sprayed or otherwise dispensed. 

Additionally, some air fresheners may use propellants that can contribute to the formation of fine particles.


Cleaning products that come in spray or aerosol forms can release fine droplets into the air. This can contribute to particulate matter in the form of liquid particles, and if the liquid evaporates quickly, it can leave behind solid particles, potentially including PM2.5.

Some abrasive or powdered cleaners, when agitated or applied, can release fine particles into the air. These particles may contribute to indoor particulate pollution.

Certain cleaning products, especially those with volatile organic compounds (VOCs) or other chemicals, can release pollutants when they undergo chemical reactions, including combustion. This combustion process may contribute to the formation of particulate matter.

A study quoted:

  • The use of cleaning products can raise the levels of VOCs in the house by 25,623%, from 64 ppb to an extremely toxic 16,565 ppb
  • Carrying out washing can raise the levels of PM2.5 from 2.2 µg/m3 to 109.7 µg/m3 – that’s nearly five times more than is present on a busy London road
  • Even a spot of ironing (using a water spray) can see VOC levels rise to concerning levels. They rose by 1,635%, from 109 ppb to 1,892 ppb


Candles and incense sticks are known to emit particulate matter, including PM2.5 when they burn. The combustion of wax or other materials in candles, as well as the burning of incense, produces small particles that can become suspended in the air. 

These particles can have health implications, especially when present in high concentrations or when exposure is prolonged.

Ironically the burning of incense sticks and candles is used widely by wellness and meditation enthusiasts who tend to be more environmentally focused but are obviously not aware of the pollution implications. 


The wear and tear of vehicle tyres can release ultrafine particles into the air, including particulate matter with a diameter smaller than 100 nanometers. These ultrafine particles are often referred to as UFPs. The release of UFPs from tyres occurs primarily due to the mechanical abrasion of the tyre tread as it makes contact with the road surface during driving. 

Tyre breaking from brake pads is also a major cause of PM2.5

Natural causes of PM2.5

Nature itself will release PM2.5. Natural processes can contribute to the release of Particulate Matter (PM), including PM2.5. Various natural sources release particles into the atmosphere, and these particles can fall into the PM2.5 category. Some of the natural sources of PM2.5 include the following:


Volcanic activity can emit ash and other particulate matter into the atmosphere, including PM2.5-sized particles. 


Natural sources include wildfires. The combustion of vegetation during wildfires releases fine particles like PM2.5, which can be carried over long distances. 


Natural processes such as wind erosion, especially in arid regions, can lift PM2.5 particles from the earth’s surface into the air. 


Mold spores, while not traditionally considered PM2.5 in the context of air quality monitoring, are indeed microscopic particles released by molds into the air. These mold spores can contribute to indoor particulate matter, and their size may vary, including particles within the PM2.5 range. 


Sea spray and waves breaking can generate sea salt aerosols, releasing small particles into the air. These are actually larger than the PM2.5 range, but atmospheric processes on these can lead to the formation of smaller particles. 

The main causes: Industrial and agricultural

The main culprits for PM2.5 (Particulate Matter with a diameter of 2.5 micrometers or smaller) in the atmosphere are typically attributed to various human activities, particularly those involving combustion processes and industrial emissions. Here are some of the primary sources of PM2.5:


Farming activities can contribute to the release of Particulate Matter (PM), including PM2.5.

The specific impact depends on various factors, including the type of farming, soil management practices, and weather conditions.

Here are some ways in which farming can contribute to PM2.5 release:

  • The mechanical disturbance of soil through tillage and plowing can result in the suspension of soil particles in the air. This can contribute to the release of PM, particularly in arid or windy conditions.
  • Farming activities such as harvesting can generate dust, especially in large-scale operations with machinery like combines and harvesters. Dust generated during these operations can contain fine particles, including PM2.5.
  • Livestock farming can also contribute to PM2.5 emissions. Dust from animal feed, manure, and bedding materials can become airborne, particularly in confined animal feeding operations (CAFOs).
  • The application of pesticides and fertilizers may involve the use of fine powders or sprays, which can contribute to the release of particles. This is more common in situations where there is inadequate management of application practices. 


Scheidel’s stoves are designed for wood burning only. This means no coal or other fuels can be used. 

The combustion of coal is a significant source of particulate matter (PM), including PM2.5. When coal is burned, especially in power plants or industrial facilities, it releases a complex mixture of pollutants into the air, and fine particles with diameters of 2.5 micrometers or smaller are part of this emission.

“More than 92% of the PM2.5 emissions were generated by the 250 largest PM2.5 emitters, of which 96.4% burned coal, 2.8% heavy fuel oil and 0.8% natural gas.“ 


The burning of waste, including plastics and other materials, releases particulate matter into the air. Also, activities like construction and demolition can generate dust, contributing to PM2.5 levels.


Combustion engines in cars, trucks, and other vehicles release PM2.5, especially in areas with high traffic density.

  • Internal combustion engines in vehicles burn fossil fuels, such as gasoline or diesel, to generate power. This combustion process produces a variety of pollutants, including particulate matter.
  • The exhaust emissions from vehicles contain a mixture of gases and particles. 
  • In addition to tailpipe emissions, the wear and tear of vehicle components contribute to particulate matter. Brake and tire wear generate fine particles that become airborne and can contribute to PM2.5 levels, particularly in urban areas with high traffic density.
  • Vehicles traveling on roads can stir up dust particles from the road surface. These particles, along with other road-related emissions, contribute to PM levels.
  • Stop-and-go traffic and idling conditions, common in congested urban areas, can lead to inefficient combustion in engines, resulting in higher emissions 

All these contribute towards the PM2.5 levels. Houses in urban areas with ventilation will see external PM2.5 sources coming into the home.,5). 


Airports can be sources of PM2.5, due to various activities associated with aviation. These can include:

  • Jet engines emit particulate matter during takeoff, landing, and while taxiing on the runway.
  •  Activities on the ground, such as the operation of ground service equipment (e.g., baggage handling vehicles, fuel trucks), can release particulate matter into the air.
  • Runway Dust: Aircraft takeoffs and landings can generate dust from runway surfaces, especially if the surface material is worn or in poor condition. This dust can contribute to PM2.5 levels.
  • Brake and Tyre Wear: The friction between aircraft tyres and the runway during landing can lead to the wear and tear of both tyres and brake systems, releasing particulate matter into the air.
  • Various vehicles operating within the airport, including buses, shuttles, and maintenance vehicles, can emit particulate matter, especially if they use combustion engines.
  • Maintenance activities, such as engine testing, can release particles into the air. The cleaning and maintenance of aircraft and facilities may also contribute. 

DEFRA air quality reports

According to The Air Quality Expert Group report, “the major sources of primary PM2.5 are combustion in the energy industries, road transport (both exhaust and non-exhaust emissions), off-road transport, residential sources and small-scale waste burning. 

They also mentioned that “the main traffic sources of PM2.5 are exhaust emissions from diesel vehicles (cars, light goods vehicles, and heavy goods vehicles), together with tyre wear, brake wear, and road surface abrasion from all vehicles.”

A recent report has also identified that further research needs to be done be done in the following subjects:

  • Emissions from domestic and commercial cooking.
  • Non-Exhaust Emissions, including brake, tyre wear (road and aviation), road abrasion, the effectiveness of heavier electric vehicles, rail track, overhead line, and brake wear.

The burning of fuel used on industrial sites, either to generate energy or to drive mobile machinery, is a major source of particulate matter emissions, accounting for 26 percent of PM2.5 emissions and 16 percent of PM10 emissions in 2021.” 

Pandemic year = Fewer cars, but no change on woodburning

The pandemic caused a notable shift in PM2.5 levels nationwide, with no local authorities projecting background pollution exceeding 10μg/m3 in 2021. Despite reduced vehicular traffic during this time, wood-burning stoves continued to be in use. 

Low stove PM2.5 emissions – Just 2.7%

New research shows that appliances that meet Ecodesign regulations account for a very small percentage of PM2.5 emissions, just 2.7%

Ecodesign stoves meet specific environmental and efficiency standards aimed at reducing emissions and improving overall performance. Schiedel’s wood-burning stoves are designed to emit lower levels compared to traditional wood-burning stoves and achieve the highest clearSkies rating and are also approved for use in Smoke Control Areas

  • Schiedel stoves are engineered to optimize combustion efficiency, ensuring that wood burns more completely. This not only increases the heat output but also reduces the amount of particulate matter emitted into the air.
  • Schiedel stoves incorporate advanced combustion technologies, such as secondary and tertiary air supplies, which facilitate more complete combustion and reduce the formation of particulate matter.
  • Schiedel stoves adhere to stringent emission standards set by regulatory bodies. These standards specify the maximum allowable levels of various pollutants, including PM2.5, that a stove can emit during operation.
  • The type of fuel used is also crucial. Schiedel stoves are designed for use with dry, seasoned wood, which combusts more efficiently and produces fewer emissions 


Elevated levels of PM2.5 stem from a diverse array of sources, including natural and heavy industry-led, as well as domestic cooking and cleaning. All of these can be more harmful to the environment and health – far more than it would by heating, using a low moisture content season wood log on a modern, energy-efficient stove

Schiedel’s stove ranges, distinguished by their efficiency and low PM2.5 emissions, substantiate this claim with their clearSkies rating and recognition as exempt products on Defra’s website.

Furthermore, installing a stove proves to be a cost-effective alternative, offering independence from reliance on gas and electricity, while circumventing the considerable expenses associated with heat pumps.

With features like secondary and tertiary air supplies, these stoves optimize the combustion process, minimizing the release of pollutants into the air. Additionally, advancements in stove design and construction ensure that they maximize heat output while minimizing wood fuel consumption, contributing to overall energy efficiency. 

The integration of cleaner-burning fuels and adherence to stringent emission standards further solidify the positive environmental profile of these stoves. As a result, they provide a sustainable and responsible choice for households seeking warmth and culinary convenience without causing a significant release of PM2.5 into the atmosphere.


Article written by Davinder Sangha, Schiedel Chimney Systems Ltd.