EPA \ TAQMN \ Air Quality Monitoring \ Photochemical Site \ Background

Background Information


With Taiwan’s economic progress and rapid population growth, large quantities of pollutants have been produced by industrial advancement and released into the atmosphere. Pollution concentration has become more severe due to rapid increase in the number of factories and automobiles. In the past decade, of the categories on the Pollutant Standards Index (PSI), SO2 has been reduced the most, while concentrations of PM10, CO, and NO2 have also been diminished greatly. However, the concentration of O3 has been increasing instead in recent years (Figure 1). O3 is a very reactive oxidizing agent and studies indicate it is harmful to the human body, building materials, and animals. It is especially damaging to the respiratory system. If a person is exposed to high concentration of ozone for a long time, symptoms such as headache, fatigue, coughing, and asthma may happen. It is also harmful to crops and also acts as greenhouse gas that contributes to climate change.

O3 is not emitted directly and is formed through nitroxides(NOX)and volatile organic molecules(VOCS)undergoing a series of photochemical reactions. Different volatile organic matters have different degrees of contribution to O3 formation. In order to understand the problem O3 causes, one needs to understand the mechanism behind O3 formation. One way to do that is to gather the information regards to the relationship between concentration of O3 precursors and O3 formations.

【Fig. 1: Average O<sub>3</sub> Concentration in Taiwan from 2003 to 2012 (unit: ppb)】
【Fig. 1: Average O3 Concentration in Taiwan from 2003 to 2012 (unit: ppb)】

Establishment of Photochemical Assessment Monitoring Stations

After the Clean Air Act Amendments were passed by the United States in 1990, local governments are required to establish Photochemical Assessment Monitoring Stations (PAMS) to monitor O3, O3 precursors, and oxygen-containing volatile organic matters to understand the reason behind concentrated O3 formation. After the implementation of the Clean Air Act Amendments started, the US Environmental Protection Agency also established other laws in 18 months to reinforce monitoring of O3 precursors, and state governments were asked to establish PAMS to monitor O3 precursors in the atmosphere and to understand nitroxides and volatile organic compounds. When the laws were reviewed and passed, PAMS were established.

The primary goal of PAMS is to provide accurate, representative, and long-term data for O3 precursors in order to establish the relationship between O3, O3 precursors, and weather conditions, to find out the factors behind O3 formation, and to devise a strategy for O3 control.

Depending on O3 formation and transport characteristics, PAMS are basically separated into 4 types: upwind and background characteristics (type 1), maximum ozone precursor concentration (type 2), maximum O3 concentration (type 3), and far downwind (type 4). As shown in Figure 2, it can be introduced in 4 points.

  1. Upwind and Background Characteristics (Type 1):The goal of this type of station is to evaluate the upwind ozone transportation information, including monitoring upwind ozone and its related precursors. This station type should be established in suitable upwind locations with high ozone precursor concentration.
  2. Maximum Ozone Precursor Concentration (Type2):This station is primarily used to monitor the maximum O3 precursor output and formation in metropolitan areas, so it should be established in the downwind direction of most of the major prevailing winds in the morning from Type 1 stations and close to locations where O3 precursors are primarily generated in metropolitan areas. If the area covered is too large, an additional station should be set up near the second major morning prevailing wind direction.
  3. Maximum O3 Concentration (Type 3): This station is mainly use to monitor the downwind area of locations where the highest concentration of O3 precursors are formed, amount of O3 formed after photochemical reactions, and VOCS remaining afterwards. It is usually set 20-40 km from city boundaries.
  4. Far Downwind (Type 4):This station type is used to understand long-distance transport of O3 and O3 precursors. It is usually established in the direction of afternoon prevailing winds and close to the edge of downwind area.
【Fig. 2: PAMS Setup Principle】
【Fig. 2: PAMS Setup Principle】

last update : 2019/11/27