Diy Air Pollution Monitor: Building A Breathable Future

Air pollution is a pressing issue in modern times, especially in urban areas with high industrialization, where harmful chemicals and pollutants in the air can cause a range of health issues, from respiratory infections to chronic diseases like lung cancer and heart disease. While there are expensive, high-end static sensor stations for monitoring air pollution, they have limitations in providing individual-level data. This has led to the development of low-cost, portable air pollution monitors that individuals can use to detect and monitor specific air pollutants like particulate matter (PM), carbon dioxide, and volatile organic compounds (VOCs). These monitors are also known as air sensors, air quality sensors, or air pollutant meters. With advances in technology, these devices have become more accessible and provide valuable insights into the complex mixture of gases, particles, and chemicals present in the air. This article will discuss the process of building a DIY air pollution monitor, covering the components, circuitry, and calibration process to provide individuals with a cost-efficient way to monitor their indoor and outdoor air quality.

Sourcing the components

Sensors

The most important components of an air pollution monitor are the sensors. Depending on your specific requirements and budget, you can choose from a variety of sensors to detect different pollutants and environmental factors. Here are some commonly used sensors and their purposes:

• PMS5003 sensor: This sensor measures PM2.5 or particulate matter in the air with a diameter of around 2.5 microns. Particulates are considered the most harmful form of air pollution as they can penetrate deep into the lungs, bloodstream, and brain, causing various health issues. This sensor works on the principle of laser scattering and usually comes with a fan to create a controlled airflow.
• MH-Z19 sensor: This sensor is used to measure carbon dioxide (CO2) levels in the air.
• MQ-131 sensor: This sensor is designed to detect ozone (O3) levels, which is an important parameter for air quality monitoring.
• MP503 sensor: This sensor can detect multiple target gases, including alcohol, smoke, iso-butane, methanal, and other Volatile Organic Compounds (VOCs). VOCs are organic emissions from everyday products like detergents, cleaners, air fresheners, paint, and makeup.

You can purchase these sensors from popular online stores like Amazon, Banggood, or AliExpress. It is worth noting that while Chinese sensors like MH-Z19, PMS5003, and DHT22 are more affordable, they may be outperformed by slightly more expensive options like Sensirion (SHT3x, SPS30) and Senseair S8 sensors, which are of European make.

Microcontroller

A microcontroller like an Arduino board is necessary to process the data from the sensors and display the information. Arduino boards are readily available online and offer a user-friendly platform for prototyping your air pollution monitor.

Power Source

To power your device, you will need a power source such as a battery or a solar panel. If you choose to use a battery, ensure it is compatible with the voltage requirements of your microcontroller and sensors. Additionally, consider using a charge controller to manage the power input and protect your device.

Enclosure

To protect your air pollution monitor, you will need an enclosure or a case. You can design and create a custom enclosure using materials like acrylic or plastic. Alternatively, you can repurpose an existing enclosure, such as a waterproof case, to house your device.

Additional Components

Depending on your design and specific requirements, you may need additional components such as wires, connectors, bolts, nuts, and other hardware. These components can be sourced from local hardware stores or online retailers.

Remember to refer to the circuit diagram and instructions specific to your chosen air pollution monitor design to ensure you have all the required components.

Building the circuitry

Building an air pollution monitor can be a complex task, but with the right tools and instructions, it is achievable. In this section, we will focus on the circuitry required to make your monitor functional.

Firstly, you will need to decide on the microcontroller board for your project. A popular choice is the Arduino UNO board, which is simple and effective for beginners. The Arduino board will serve as the brain of your air pollution monitor, allowing you to process data from sensors and display it accordingly.

Next, you will need to gather the necessary sensors for your device. The sensors you choose will depend on the specific air pollutants you want to measure. Some common sensors include the PMS5003 for particulate matter (PM2.5), MH-Z19 for carbon dioxide (CO2), and DHT22 for temperature and humidity. These sensors will need to be connected to your Arduino board according to the circuit diagram provided by the manufacturer. Ensure you have a detailed understanding of the circuit diagram before proceeding, as incorrect connections can damage your components.

Now, let's discuss the power requirements. Your circuit will require a consistent power source, and fortunately, the Arduino board can be easily powered using a common adapter that provides an input voltage of 5V. This power source will ensure that your sensors and microcontroller have the energy they need to operate. Additionally, you will need to consider airflow and overheating. A small fan can be included in your circuitry to prevent your device from overheating during operation.

Finally, you will need to calibrate your sensors. This process involves comparing your device's readings with those of a calibrated master device. By doing so, you can adjust the sensitivity and accuracy of your sensors to ensure they provide reliable data. One example of a calibrated master device is the TSI IAQ Q-Trak 7585, which can be used as a reference for indoor air quality monitoring projects.

Calibrating the sensors

Choose the Right Sensors

Select sensors that are suitable for the specific air pollutants and environmental factors you intend to measure. Common pollutants measured include particulate matter (PM), carbon dioxide, carbon monoxide, and volatile organic compounds. Consider factors such as sensitivity, accuracy, and durability when choosing your sensors.

Understand Sensor Characteristics

Each type of sensor has distinct characteristics, and it is important to understand how they interact with the environment. For example, some sensors may be sensitive to temperature changes, while others may require heating. Understanding these characteristics will help you make informed decisions during calibration.

Calibration Techniques

There are several calibration techniques available, including traditional linear regression models and more advanced machine learning-based approaches, such as random forest models. Machine learning techniques have shown great promise in improving the accuracy of low-cost sensors and their ability to calibrate sensors in-field.

Spatial Calibration

Spatial calibration takes into account the location of the sensors and individual calibration coefficients. This is particularly important for low-cost sensors as their accuracy can be affected by their specific placement and the environmental conditions of that location, such as high relative humidity.

Reference Measurements

To ensure accurate calibration, reference-grade measurements are necessary. This can be done by comparing the readings from your sensors with those from regulatory stations or standard particle concentration measurement devices. This helps to identify any biases or inconsistencies in your sensors' readings.

Periodic Recalibration

Low-cost sensors may suffer from accuracy degradation over time due to various factors, including cross-sensitivities to different pollutants and external influences like weather changes. Therefore, it is important to perform periodic recalibration to maintain the accuracy of your air pollution monitor. The frequency of recalibration can depend on various factors, and a single calibration cycle can improve accuracy for up to two weeks.

By carefully calibrating and maintaining your sensors, you can improve the accuracy and reliability of your air pollution monitor, allowing you to gain valuable insights into the air quality in your environment.

Creating the enclosure

To create the enclosure for your air pollution monitor, you will need to carefully follow the steps outlined below:

Firstly, decide on the size and shape of your enclosure, taking into consideration the number of sensors you plan to include and their placement. A plastic enclosure is a good option, as demonstrated by a user on howtomechatronics.com, who reported success with this material. You can also print a small temperature probe that can be attached to the enclosure, allowing for more accurate temperature readings by minimising the impact of the heat that builds up within the main enclosure.

Next, gather the necessary tools and materials. This may include a soldering iron, solder wire, a multimeter, a breadboard, and a variety of electronic components such as capacitors, resistors, transistors, and sensors. If you are new to electronics, it is recommended to familiarise yourself with the components and their values before proceeding.

Once you have all the necessary materials, you can begin assembling the enclosure. This may involve soldering the sensors onto a printed circuit board (PCB) or using a breadboard to connect the components. The PCB can be designed using software such as EasyEDA, and the Gerber files can be used to order custom PCBs if desired. It is important to note that if you use a display or RGB LED shield, you will need to solder the D1 Mini directly onto the PCB without the pin headers, as they will cause the assembly to become too tall and not fit within the enclosure.

Additionally, consider the placement of the sensors within the enclosure. For example, when soldering the CO2 sensor, ensure that the bottom side has enough airflow. You may also need to solder small pins onto certain modules, such as the SHT30/31 module, using a breadboard to fix it in place before soldering it onto the board.

Finally, connect the sensors and components according to the circuit diagram provided for your specific project. This may involve powering the sensors and connecting them to a microcontroller or development board, such as an Arduino. Ensure that you follow the provided code and make any necessary adjustments for your specific setup.

By carefully following these steps and referring to the specific instructions for your chosen air pollution monitor project, you should be able to successfully create the enclosure for your device.

Testing and troubleshooting

Calibration and Sensor Testing

Calibration is essential to ensure the accuracy of your air pollution monitor. Compare the readings of your device with those of a calibrated professional device or a trusted reference source. For example, you can use a calibrated master device like the TSI IAQ Q-Trak 7585 to simultaneously measure air quality and compare the readings. Additionally, you can refer to air quality data provided by government agencies or reputable organizations in your region. By matching the readings of your device with these trusted sources, you can identify any discrepancies and make the necessary adjustments.

Sensor Functionality

Test each sensor individually to ensure they are functioning correctly. For instance, if you're using an MH-Z19 sensor for CO2 detection, check its readings against known CO2 concentrations. You can generate CO2 by blowing your breath into the sensor, and the readings should reflect the increased CO2 levels. Similarly, test other sensors, such as the PMS5003 for particulate matter (PM2.5) or the MQ-131 for ozone detection, by exposing them to controlled environments with known pollutant concentrations.

Environmental Factors

Consider the impact of environmental factors such as temperature and humidity. The accuracy of your air pollution monitor can be influenced by these variables. Test your device in different temperature and humidity conditions to observe any deviations in readings. For example, you can place your device in a controlled environment, like an air-conditioned room, and compare the readings to those from a trusted source. If there are significant differences, you may need to calibrate your device for these specific conditions.

Placement and Ventilation

The placement of your air pollution monitor can affect its readings. Test your device in different locations within the indoor space to identify any discrepancies. For example, place the monitor near a window or door and observe the readings when there is increased ventilation. Then, move it to a more enclosed area and compare the results. This will help you understand how air circulation influences the accuracy of your device.

Data Processing and Connectivity

Ensure that the data processing methods are accurate and reliable. Check the device's instructions or consult the manufacturer to understand how the data is processed and presented. Additionally, if your device connects to an app or software, ensure that the connectivity is stable and that the data transmission is accurate. Regularly update the device's firmware and app to improve performance and address any known issues.

Maintenance and Lifespan

Air pollution monitors have a limited lifespan, and their performance may degrade over time. Regularly clean and maintain your device according to the manufacturer's instructions. Keep track of how long the device has been in use and be mindful of any recommended servicing or replacement intervals provided by the manufacturer. As sensors age, their accuracy may decline, and they may need to be recalibrated or replaced to ensure reliable readings.

Health Considerations

If your air pollution monitor detects elevated levels of pollutants, consider the potential health implications. Consult with healthcare professionals or refer to guidelines from organizations like the Environmental Protection Agency (EPA) to understand the health effects of specific pollutants. While elevated readings may not always indicate an immediate health risk, they can guide you in taking preventative measures, such as increasing ventilation or consulting specialists for further advice.

Remember, the accuracy of low-cost air pollution monitors can vary, and it's important to stay informed about the limitations of your device. By regularly testing and troubleshooting, you can ensure that your air pollution monitor provides reliable data, enabling you to make informed decisions about your indoor air quality.

Frequently asked questions