# A Review of Air Pollution Monitoring Technology for Ports
## 2 Detection Methods for Air Pollutants in Ports
### Air Pollutant Sample Collection  
In air pollutant monitoring, air sampling is an important part of the monitoring process, and the collection methods of air pollutant samples can be summarized into two categories: direct sampling method and enrichment (concentration) sampling method [22]. When the concentration of the measured component in the air is high or the analytical method is sensitive, the direct sampling method is used. The direct sampling method is a gas sampling method in which gas samples are collected directly in gas sampling bags or vacuum bottles and other containers and then are brought back to the laboratory for analysis and testing; the common sampling containers are syringes, plastic bags, and some fixed containers, etc. They are used to measure instantaneous concentration of pollutants in the air or the average concentration over a short period. When the concentration of the measured component in the air is low, the enrichment sampling method is used. The enrichment sampling method, also known as the concentration sampling method, is the collection of air samples to be measured in the concentration of components enriched in the absorption medium and then analyzed and tested methods, including the solution absorption method, filling small column sampling method, low-temperature condensation method, and filter sampling method. The sampling time of this method is generally longer, and the average concentration of pollutants in the atmosphere during the sampling time is measured, which can better reflect the real pollution situation of the atmosphere in a period of time [23; 24; 25]. According to the different power used to collect air pollutants, the enrichment sampling method can be divided into active sampling method and passive sampling method. The active sampling method is a method in which the sampling pump makes the air sample pass through the sampling tube or absorption bottle containing the absorption medium so that the pollutant gas to be measured in the air is concentrated in the absorption medium. According to the different absorption media, it can be divided into solid active sampling method and liquid active sampling method. Additionally, the passive sampling method is a concentrated sampling method based on the principle of molecular permeation or diffusion to enrich the air with polluting gases. The passive sampler using this method can be divided into two types: infiltration type and diffusion type according to the different gas enrichment principles [26; 27; 28]. In general, the method of air sampling needs to be chosen according to the purpose of sampling and the site conditions to ensure that the quality of the collected samples meets the monitoring needs. For port air pollution monitoring, for example, because the direct \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Port Development** & **Project Type** & **Air Pollution Sources** & **Main Pollutants** \\ \hline \multirow{6}{*}{Operation Period} & \multirow{6}{*}{Port transportation equipment} & Construction machinery emissions & \multirow{2}{*}{SO\({}_{2}\), NOx, CO, \multirow{2}{*}{HCP, \multirow{2}{*}{Fumes and dust}} \\  & & Transport vessel emissions & \\  & & Loading and unloading machinery and & \\  & & vehicle emissions & \\  & & Evacuation vehicle emissions & \\ \cline{2-4}  & & Transport, storage, loading and & \\  & & unloading of coal and ore in the port area & \\  & & Dust from the road & \\ \cline{2-4}  & & Container & Large-scale container lifting equipment & \\  & & Terminal & Container transport equipment & \\ \cline{2-4}  & & Petrochemical & \\  & & Liquid bulk transfer and storage & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._sampling method for the sample container sealing and chemical inertness requirements are high and are often used in the case of high concentrations of air pollutants, taking into account the environmental conditions in the port and on board the ship, the direct sampling method is generally not applicable.