Ambient Assessment. Why monitor?

Air pollution is a complex mixture of various chemical compounds in the form of solid particles, liquid droplets, and gasses. According to EEA the key air pollutants include particulate matter (PM), ground-level ozone (O3), nitrogen dioxide (NO2), sulfur oxides (SOx), and heavy metals. Moreover, construction activities, particularly those involving heavy machinery and equipment, contribute to physical pollution such as noise and vibrations.  

By prioritizing sustainable construction practices, such as transitioning to low-emission technologies and CO2-reducing energy systems, increasing operational efficiency, and establishing air quality monitoring networks around construction zones, it is possible to mitigate the adverse effects of construction-induced air pollution effectively with actionable data. 

Benefits of real-time ambient monitoring: 

• Safeguarding the health and safety of construction site workers;
• Documenting regulatory compliance with national and local authorities for the environment;
• Building transparent and trust-based relationships with nearby communities;
• Understanding short-term changes in air quality and indicating what activities should be improved;
• Resource optimization - reduced usage of dust suppression solvents;
• Data-driven decisions, especially for workplace safety.

Monitoring using lower-cost sensor network

Construction site environment 

Construction processes can occur outdoors and indoors depending on the project and its stage. Activities outdoors occur in the open environment; ambient monitoring during this phase might focus on parameters like dust generation, noise, and vibrations caused by heavy machinery and equipment. Moreover, monitoring weather parameters, such as wind, rain intensity, and solar conditions is also beneficial. Beyond understanding the spread of pollution from the construction site, it also enables construction teams to implement proactive safety measures during adverse weather events: 

• Strong winds - Stop work at height. Bring down all the workers and stop crane work.
• Heavy rain - Maintain soil integrity. Document the days that work could not be conducted. 

The construction site is inherently dynamic and characterized by its rough nature. Study results show that the construction industry contributes substantially to pollution, accounting for 30% of particulate matter (PM10) emissions, 8% of fine particulate matter (PM2.5) emissions, and 4% of nitrous oxide emissions.

Recognizing that effective management hinges on accurate measurements, understanding pollution levels affecting the construction site and surrounding communities is essential.

Planning 

To get the most out of the investment of time and money, it is important for those using low-cost air sensors to understand what they can and cannot do and the factors that need to be considered for air sensor network design. Careful planning can improve the chances of the data collected fulfilling the aims of a project.

Planning considerations:

• Clearly define specific questions to be answered, such as: characterizing known air pollution sources, assessing personal exposure, or informing stakeholders.
• Define the pollutants to be monitored and their typical concentration ranges (if known). 
• Consider additional resources to understand better the influence of other factors on the data quality - installing a background air sensor, and having a sensor for detecting vibrations.
• The monitoring of the weather conditions, including rain, wind speed, and wind direction, is very important to understand pollution transport from construction sites and safe work conditions.
• Determine the necessary spatial and temporal resolution to achieve monitoring goals effectively.
• Identifying how data will be collected and stored, and who will have access to it.
• Establishing quality assurance and control (QA/QC) measures is essential to maintain the reliability and accuracy of the data.
• Evaluate available and suitable installation positions for air sensors based on existing infrastructure. Ensure the necessary tools and accessories are available for installation.
• Define the project team roles, including those who will access and manage the data, install devices, monitor performance, and conduct field maintenance of air sensors.
• Summarize the timeline of the project and expected outcomes.
• Determine backup plans for changes, e.g., change in staff, sensor failure or destruction etc.
• Allocate budgetary resources for the procurement, installation, data quality control and data analysis, and maintenance of the air quality monitoring network.

Air sensor network density

To decide on how many air sensors to install on the site, it might help to consider some questions about why and where to collect measurements, such as:

• What types of changes in air quality are expected in the area?
• A uniform construction site may require up to five sensors to ensure adequate coverage of all wind directions; 
• If there are some “points of interest”, i.e. specific machinery, untypical material handling, chemical compounds, etc., then additional sensors should be installed in those spots;
• If there are certain actions intended to reduce air pollution it is important to have sensors before and after to get a representative assessment of the action effectiveness.
• What is the typical or prevailing wind flow in the area and how might winds transport pollutants*? 
• It is advisable to position sensors downwind to ensure that most of the pollution will be registered by sensors.
• Is weather data necessary to interpret air quality data? It is particularly important for the sites that: 
• are sensitive to soil stability or flooding;
• are sensitive to excess amounts of water; 
• have crane on-site and work performed at heights;
• are sensitive to droughts or excessive sun exposure.
• or to acquire high-quality data: water particles can be mistaken for PM spikes during rain due to condensation on solid particles forming aerosols.
• What is the budget for air sensors?
• Using low-cost sensors for 3-4 device network hardware starts 20-30k DKK for hardware;
• In most cases, the monthly fees for data collection, storage, and maintenance add up.

Using a map or other drawing that represents the prospective monitoring site to point out general locations for air sensors might be a great help. The following should be considered:

• Spread out the deployment locations to get good spatial coverage**.
• Avoid hyperlocal sources (e.g., smoking areas) and locations where winds can channel pollutants unless that is a research question
• If there is an area of concern (e.g. suspected areas of increased concentrations, etc.) locate sensors near/inside it and both, upwind and downwind of the area so that meaningful comparisons can be made.
• Pinpoint the location of the background air sensor. 

* applicable for outdoor measurements

** A good spatial coverage refers to a distribution of sensors that effectively covers the entire area of interest, ensuring that the sensors would capture a representative and comprehensive picture of the ambient conditions. It depends on the scale and intricacies of the site and the goal of the monitoring. E. g. If a significant variation in ambient parameters is expected within short distances, a higher density of sensors might be necessary for better coverage. In contrast, in a larger outdoor area with more uniform conditions, sensors may be spaced at greater distances. It's essential to consider the nature of construction activities and potential pollutant sources.

Installing lower-cost AQ monitoring equipment

After the installation sites have been selected, there are a few more points to consider.

Adapted from EPA

Data presentation

Air sensor users may wish to communicate their findings to a variety of different audiences including members of their community, regulators, partners, or others. Thus, understanding how the gathered data addresses predefined questions or fulfills monitoring objectives is critical for the effective communication of project outcomes.

Interpreting air pollution data can be complex due to the varied limits set by various regulation bodies. Data collection, display, interpretation, and public relay should be planned at the project's outset. For example, by aggregating data, one can notice trends and patterns in the data. Moreover, some averages will be more relevant to the investigation than others (e.g. to compare data with standards, the aggregation should be similar to the aggregation required by the standard). 

Data presentation should be easily understood. There are many ways to visualize data (e.g., graphs, tables, charts, animations). How you choose to display your data may be based on your project objective and/or the audience you are sharing your results with. One of the easiest ways to make data easy to understand for technical and non-technical audiences is to create a dashboard that displays all data visualizations in one place.

Another way to analyze and present data is through reports. It is a good idea to evaluate the need for regular reports to keep stakeholders informed about the project status or particular events on-site.

In case of any doubts, it might be useful to speak to someone with specialist knowledge of air pollution. Consider whether training or educational resources for the project team members are necessary for effective data interpretation and presentation.

Maintenance of the network

While sensor networks offer numerous benefits, they are susceptible to malfunctions that can lead to data loss or poor-quality data. Preventative actions associated with maintenance are necessary for both short- and long-term operations. Steps to minimize sensor failures:

• Address sensor management questions before deploying the network;
• Implement routine maintenance and a logbook to ensure regular maintenance intervals;
• Schedule field calibration and correction to ensure sensor accuracy;
• Register sensor failures promptly to minimize data loss (alarm/notification system in place);
• Continuously monitor sensor network data and functionality for early detection of issues (odd patterns, decreased response, drift, etc). Instrument problems tend to produce data that often look too regular, or change too abruptly to be due to natural atmospheric phenomena;
• Replacement of the sensor when it fails or reaches the end of its service lifespan;
• Conduct site visits to assess and address physical conditions affecting sensor health;
• Replacement of filters and other consumables like batteries if used;
• If solar panels are used, incorporate periodic maintenance to remove dust, ensuring efficient power generation.

To ensure the sustained functionality of the sensor network, the construction company or project team member must take an active role in these maintenance tasks. Alternatively, a third-party sensor provider with comprehensive services can streamline these maintenance processes, offering an all-encompassing solution for hassle-free operation. This collaborative effort ensures the longevity and accuracy of the sensor network, contributing to reliable data collection and effective monitoring.