# A Survey of Wireless Sensor Network Based Air Pollution Monitoring Systems
## 3 Air Pollution Monitoring Equipment  
Conventional air pollution monitoring systems are mainly based on sophisticated and well-established instruments. In order to guarantee the data accuracy and quality, these instruments use complex measurement methods [44] and a lot of assisting tools including temperature controller (cooler and heater), relative humidity controller, air filter (for PM), and build-in calibrator [45]. As consequences, these instruments are typically with high cost, high power consumption, large volume, and heavy weight. Thanks to technology advance, ambient sensors with low cost, small size and fast response time (in the order of seconds or minutes) is available recently. However, no low-cost portable ambient sensor can achieve the same data accuracy and quality as conventional monitoring instruments [46] (see Tables 5 and 6). Currently, the air pollution data at locations without monitoring stations are obtained by air quality models or estimations [20]. However, the data from the air quality models lack of cross-validation and verification. The low-cost portable ambient sensors provide a huge opportunity in increasing the spatio-temporal resolution of the air pollution information and are even able to verify, fine-tune or improve the existing ambient air quality models. In the following subsections, the working mechanisms of the low-cost portable ambient sensors that are widely used in TNGAPMS are introduced. As a matter of fact, except the air pollution detecting technologies mentioned in Sections 3.1 and 3.2, there are other detecting technologies such as Surface Acoustic Wave (SAW) [47, 48, 49], Quartz Tuning Fork (QTF) [50, 51], Raman Lidar [52, 53] and Differential Ultra Violet Absorption Spectroscopy (DUVAS) [54, 55] that we will not discuss for unpopularity reason. \begin{table}
**Health Risk Category** & **AQHI** \\ \hline \hline Toy (Green) & 2 \\ \hline \hline \end{tabular} \
\begin{tabular}{|c|c|} \hline \hline \multirow{2}{*}{Toy (Green)} & 4 \\ \cline{2-3}  & 5 \\ \cline{2-3}  & 6 \\ \hline \hline High (Red) & 7 \\ \hline \hline \end{tabular}
\begin{tabular}{|c|c|} \hline \hline \multirow{2}{*}{Toy (Green)} & 8 \\ \cline{2-3}  & 9 \\ \cline{2-3}  & 10 \\ \hline \hline
**Serious (Bisks)** & 10+ \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Air Quality Health Index (AQHI) of Hong Kong Environmental Protection Department. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Pollutant** & **Example Product** & **Measurement Method** & **Resolution** & **Accuracy** & **Range** & **Price (USD)** \\ \hline \multirow{4}{*}{PM\({}_{2.5}\)} & Met One Instrument BAM-1020 & \multirow{2}{*}{Beta Attenuation} & \multirow{2}{*}{1 \(\mathrm{\mu g/m^{3}}\)} & \multirow{2}{*}{\(\pm\)1 \(\mathrm{\mu g/m^{3}}\)} & \multirow{2}{*}{0-1000 \(\mathrm{\mu g/m^{3}}\)} & \multirow{2}{*}{About \$25,000} \\  & Beta Attenuation Monitor [56] & & & & \\ \cline{2-6}  & Met One Instrument & & & & \\ \cline{2-6}  & Aeroet 831 Aerosol Mass Monitor [57] & & & & \\ \cline{2-6}  & Alphasense & & & & \\ \cline{2-6}  & OPC-N2 Particle Monitor [58] & & & & \\ \cline{2-6}  & Sharp Microelectronics & Light Obscuration & & & \\ \cline{2-6}  & DN/C3 CA006 PM2.5 Module [59] & & & & \\ \hline \multirow{4}{*}{PM\({}_{10}\)} & Teledyne Model 602 BetaPLUS & \multirow{2}{*}{Beta Attenuation} & \multirow{2}{*}{0.1 \(\mathrm{\mu g/m^{3}}\)} & \multirow{2}{*}{\(\pm\)1 \(\mathrm{\mu g/m^{3}}\)} & \multirow{2}{*}{0-1500 \(\mathrm{\mu g/m^{3}}\)} & \multirow{2}{*}{About \$530,000} \\  & Particle Measurement System [60] & & & & \\ \cline{2-6}  & Met One Instrument & & & & \\ \cline{2-6}  & Aeroet 831 Aerosol Mass Monitor [57] & & & & \\ \cline{2-6}  & Alphasense & & & & \\ \cline{2-6}  & OPC-N2 Particle Monitor [58] & & & & \\ \cline{2-6}  & Sharp & Light Obscuration & & & & \\ \cline{2-6}  & GP2Y1010 AU Air Quality Sensor [61] & & & & \\ \hline Lead (Pb) & Operation in Lab & - & - & - & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Instruments used in air quality monitoring systems (Part A).