Air Particulate Monitoring – PM1

What is PM₁

“PM” (Particulate Matter) is not a single pollutant, but refers to a complex mixture of solids and aerosols of varying shape, size, and chemical composition and may contain many chemical species like organic compounds, inorganic ios, metallic compounds, elementary carbon, etc. 

These atmospheric particles are defined by their diameter for air quality regulatory purposes.

The ultra-fine inhalable particles that are less than or equal to 1 micrometre in diameter are collectively known as PM₁. They are more than 400 times thinner than a human hair (too small to be detectable by the human eye) that can penetrate directly through lungs into the bloodstream when inhaled. 

PM₁ are extremely fine particles and a major subset of PM_2.5 that are likely to reach deeper into the body than PM_2.5, making them even more harmful as they can reach other organs through the bloodstream.  PM₁ particles in the atmosphere remain suspended into the air due to their negligible mass making it more susceptible to exposure. Because of their very small size, PM₁ undergoes various transformations due to either coagulation, condensation, evaporation, and/or deposition in the atmosphere. They are ultimately removed after a long time mainly by activation in clouds and subsequent precipitation.

Sources

Particulate matter PM₁ are either directly emitted from a source (primary PM) or are formed through the chemical reactions of gases such as oxides of sulfur (SO_x), nitrogen oxides (NO_x), organic compounds, etc. in the atmosphere (secondary PM). The natural sources of PM₁ particulate matter are marine aerosol, soil erosion, volcanic eruptions, and forest fires. Anthropogenic sources of PM₁ include:

• Burning fossil fuels such as gasoline, oil, diesel, coal or wood, etc. 
• Agricultural processes
• Cooking and cigarette smoke. 
• Emission from motor vehicle exhaust, specifically diesel-powered.
• Emission from power plants and industrial combustion processes

Secondary PM₁ is generally formed via photochemical reactions of gases and condensation of semi-volatile vapors in the atmosphere. They usually consist of sulfuric acid, ammonium sulfates and nitrates, organic compounds, and a range of trace metals. 

Health & Environmental Impact of PM₁

Health Impact

The potential of the particulate matter to affect human health depends directly on the size of particulate matter. When inhaled, the particles with up to 2.5 μm diameter generally pass through the nose and throat and travel deep into the lungs through the respiratory tract. However, PM₁ particles i.e. particles with diameter < 1 μm, are so small that they can travel deeper into the lungs to the alveoli (i.e. the tiny sacs in the lungs where O₂ and CO₂ are exchanged). Some PM₁ particles pass through the alveoli cell membranes and enter the bloodstream and can reach to other parts of the body. They can damage the inner walls of the arteries and can penetrate the tissues, potentially spreading through the organs and damaging them. 

When inhaled for short periods, PM₁ irritates the eyes, nose, throat, and upper respiratory tracts, coughing, sneezing, and shortness of breath. It aggravates already present respiratory diseases such as asthma and can result in premature mortality, acute and chronic bronchitis, other respiratory symptoms, etc. 

Exposure to PM₁ pollution, for a long period (i.e. months or years), can cause permanent respiratory problems such as asthma, chronic bronchitis, and heart disease and cause reduced lung function growth in children. Prolonged exposure of PM₁ contributes to severe diseases like heart attacks, lung cancer, edema, etc. leading to premature death. 

Environmental impact

The major environmental impacts of PM₁ pollution are visibility reduction and smog. Particulate matter, specifically the ones with a diameter < 2.5 μm alters the absorption and scattering of light in the atmosphere affecting visibility. Additionally, the settling of the air-borne particles on plants, soil, and water ecosystems have harmful effects on them. The metal and organic compounds reduce plant growth and yield while the deposition of PM into water bodies affects its quality and clarity. 

Atmospheric particles affect the heating and the cooling of the atmosphere. Some components of PM such as black carbon promote climate warming while some components such as sulfates and nitrates have cooling properties. These particles are also the major precursors of smog.

Possible corrective measures 

The primary step is air particulate monitoring to identify the areas with high particulate levels. In addition to this, the following corrective measures can be taken:

• Limit outdoor activities and close windows and vents during times of high air pollution.
• Avoid keeping your vehicle idle for long. 
• Avoid areas with traffic congestions, construction activities, or unpaved roads. Breathing such polluted air daily also leads to health effects in the long run. 
• Eliminate the use of the fireplace, wood stove, gas-powered lawn, or garden equipment. 
• Eliminate open burning of leaves, trash or other materials

Measurement methods of air particulate monitoring

Different working principles for air particulate monitoring in the ambient environment are Gravimetric, Beta Attenuation (BAM), and Laser scattering. 

High-volume Gravimetric Method – The air particulate monitors based on the gravimetric principle takes in the ambient air for 24 hours at a constant flow rate through a size-selective inlet that only allows particulate matter with an aerodynamic diameter of 1µm or less to pass through. The particulate matter is collected onto a pre-weighed filter conditioned at constant temperature and humidity conditions. After the 24-hour sampling period, the filter is conditioned again under the same temperature-humidity conditions and reweighted. The difference in the weight corresponds to the mass collected on the filter, which along with known flow-rate, sampling period, and the total volume of the air sampled is used to calculate the PM₁ concentration. 

Beta Attenuation Monitor (BAM) – The air particulate monitoring based on the BAM principle measures the particle mass density using beta radiation attenuation. The particulates in the ambient air drawn into the air particulate monitor are deposited on a paper-band filter and exposed to beta rays (i.e. electrons with energies in the 0.01 to 0.1 MeV range) which get attenuated as a function of the particulate mass. The beta count reduces with an increase in the PM₁ mass and is recorded by the detector and converted to concentration.

Laser Scattering – The air particulate monitor based on the physical principle of light scattering, also known as optical particle counter (OPC), measures dust particles illuminated by laser light at a 90° angle. The light scattered from each particle is collected at approximately 90° by a mirror and detected by a photo-diode. This signal is then fed into a multi-channel size classifier where a pulse height analyzer is used to classify each pulse that is proportional to the particle size. The counts in the channel corresponding to PM₁ are converted to the concentration of PM₁.

Among all the above principles of air particulate monitoring, PM monitors based on laser scattering are typically found to be preferred for ambient air monitoring as they yield quick and accurate measurements and are inexpensive in comparison with the others.

Oizom’s working principle for air particulate monitoring

Oizom’s DUSTROID is an online particulate monitoring system that measures the concentration of various particulate sizes ranging from 1 micron to 100 microns such as PM_1, PM_2.5, PM₁₀, and PM₁₀₀ in the ambient air. Our PM sensor works on the principle of laser scattering. The active sampling powered sensor-based air quality monitor DUSTROID is deployed across several cities, campuses, universities and is used for drawing actionable insights to tackle the rise in ambient PM₁ concentrations.

5 reasons why air particulate monitoring is important

• PM₁ is a complex mixture of microscopic solids and aerosols that can easily pass through the nose and throat, penetrate deep into the lungs and enter the bloodstream reaching other organs of the body. 
• Particulate matter is emitted into the atmosphere from vehicular exhaust, power plants, combustion processes such as the burning of fossil fuels, waste, etc. They are also formed into the atmosphere from various chemical reactions of other air pollutants such as NO_x and SO_x. 
• When inhaled, it irritates the eyes, nose, throat, and the airways and can penetrate tissues causing severe diseases like heart attacks, lung cancer, edema, etc. leading to premature death. , etc.  
• Air particulate monitoring is an efficient way to detect high concentrations of particulate matter and prevent high-level exposures.
• Real-time air particulate monitoring helps in determining the quality of air as well as formulating an action plan to control high levels of PM pollution.