Air pollution is one of the most important factors affecting the quality of life and the health of the increasingly urban population of industrial societies. In many cities, the air is polluted by emissions from sources such as cars and trucks, power plants, and manufacturing processes. When gases and particles from those activities accumulate in the air in high enough concentrations, they can be harmful for human health, an environment. Often, terrain and meteorological conditions complicate air quality issues in the area. Although the national trend is toward better outdoor air quality, there are some urban areas in which no improvement has taken place. Concentrations of outdoor air pollutants vary from day-to-day and even during the course of a day.
For health protection, the public needs timely information about air quality and other factors (e.g., weather conditions) that affect it. An access to air quality forecasts allows residents to reduce their exposure when the pollutant concentrations are high. This is important particularly to people who are sensitive to certain pollutants’ harmful effects. For example, people with asthma may be sensitive to ground-level ozone and sulphur dioxide. The major motivation behind our study and the development of the system is to help the government to devise an indexing system to categories air pollution in India. The project is to build an air pollution monitoring system, so a detection system for multiple information of environment is designed in this project. This project is built for low cost, quick response, low maintenance, ability to produce continuous measurements. The main goal of this project is to monitor the air pollution, hazardous gases and increase awareness about pollution by using air pollution monitoring system. Present state of the air quality control in almost all industrial centers in our country is based on taking samples one or few times a day, which means that there is no information about time distribution of polluted materials intensity during day. This is the main disadvantage of such system.In the area, there are two methods to use to monitor air pollution at present. The one is passive sampling (nonautomatic), and the other is continuous online monitoring (automatic). The advantage of the passive sampling method lies in that the monitor equipment is simple and inexpensive, but it can only get on-site monitoring parameters in a certain period, cannot provide real-time values. Meanwhile, the results of monitoring effect by the man factor largely and it will seriously damage the health of the monitoring man in the site of high concentration of harmful substances.
The procedure of continuous monitoring method is as follows: use sensors to monitor the parameters, and then send to the control center by network. The way of data transfer include both wired and wireless. The wired way usually uses public telephone network, or fiber-optic to realize data transmission. Although this method is stable and reliable, with high speed of data transmission, but the shortcomings of the method is also obvious in a wide and dynamic range. With the rapid development of communication technology, network technology and remote sensing technology, there is a trend that air pollution monitoring system is often designed in wireless mode. At present, the wireless mode in air pollution monitoring system includes GSM, GPRS, etc. But these modes are high cost in both installation and maintenance, and complexity. In the other hand, Wireless sensor network have been rapidly developed during recent years. Starting from military and industrial controls, its advantages include the liability, simplicity, and low cost. Based on these advantages, it is now being applied in environmental monitoring. In air pollution monitor applications, we have designed a WSN based air pollution monitoring system using ZigBee networks for City. They focus on implementation of air pollution monitoring system, and developed an integrated wireless sensor board which employs CO2, NO2/NH3 temperature sensor, atmega16 micro-controller, database server and a ZigBee module.
2. System Overview
2.1 Proposed System
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Figure 1:Proposed system scenario
The working of proposed Air pollution monitoring system as follows:
1. Develop architecture to define nodes and their interaction.
2. Collect air pollution readings from a region of interest.
3. Collaboration among thousands of nodes to collect readings and transmit them to a gateway, all the while minimizing the amount of duplicates and invalid values.
4. Use of appropriate data aggregation to reduce the power consumption during transmission of large amount of data between the thousands of nodes.
5. Visualization of collected data from the WSN using statistical and user-friendly methods such as tables and line graphs.
6. Provision of an index to categorize the various levels of air pollution, with associated colors to meaningfully represent the seriousness of air pollution.
7. Generation of reports on a daily or monthly basis as well as real-time notifications during serious states of air pollution for use by appropriate authorities
2.2 Hardware Architecture
The proposed system is designed by integrating the following hardware modules shown in Fig. 2. As the figure shows, the system consists of a ATMEGA16 microcontroller integrated with a sensor array using analog ports. The hardware unit is also connected to a GPS module and a ZigBee-Modem using the RS-232 interface. Each of these components is described in the following
2.2.1. ATMEGA16 microcontroller
The ATMEGA16 microcontroller is the main component of a pollution detection unit. The operating system that runs inside the chip coordinates the substances measurement process, the
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Figure 2: System hardware basic building blocks
acquisition of the GPS coordinates and the data transmission to the central server. The microcontroller is mounted on a development board that provides an RS232 serial communication to the ZigBee modem and ZigBee receiver and a parallel connection to the gas sensors. The connection between the gas sensors and the ATMEGA16 microcontroller can’t be made directly because of the very small output voltages provided by the sensors (mA).This problem is solved by using auxiliary electronic circuits for signal conversion like OA (Operational Amplifiers) and transistors.(see Figure 2)
2.2.2. Sensors Array
The sensor array consists of two air pollutions sensors including Carbon Dioxide (CO2), Nitrogen Dioxide (NO2). As Table I shows, the resolution of these sensors is sufficient for pollution monitoring. Each of the above sensors has a linear current output in the range of 4 mA–20 mA. The 4 mA output corresponds to zero-level gas and the 20 mA corresponds to the maximum gas level. A simple signal conditioning circuit is designed to convert the 4 mA–20 mA range into 0–5 V to be compatible with the voltage range of the built-in analog-to digital converter in the ATMEGA16 microcontroller. (see Figure 1,2)
2.2.3. ZigBee Modules
In this paper, two types ZigBee modules are used to organize a network for air pollution monitoring system. The network is controlled by devices called the ZigBee coordinator modem (ZCM). The ZCMs are responsible for collecting data and maintaining the other devices on the network, and all other devices, known as ZigBee end devices (ZED), directly communicate with the ZCM. The ZigBee module is hardware platform of wireless device. The modules realize the basic function of Physical and MAC layer, such as transmit and receive, modulation and demodulation, channel and power control. They operate at 2.4GHz frequency ISM band wireless communication. The modules include a digital direct sequence spread spectrum base band modem and an effective data rate of 250 kbps. They employ the EM2420 2.4GHz radio frequency transceiver and the ATMEL 8-bit AVR microcontroller. They also exhibit a nominal transmit of -1.5dBm and a receive sensitivity of -92dBm When powered at 3.0V, the modules draw 31.0mA in transmit mode and 28mA in receive mode. When the entire module is in sleep mode, the current draw is reduced to approximately 10uA.(see figure 1,2)
Table 1. Sensor Specification
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2.3.4. Central Server
The Central-Server is an off-the-shelf standard personal computer with accessibility to the Internet. The Pollution Server is connected to the ZigBee-Modem via RS-232 communication standard. The air pollution information sent from each ZED are collected to ZCM. And then the data are saved to database of central server.(see figure 1)