1. Introduction
With the development of modern industry, industrial equipment and transportation vehicles consume lots of resources and discharge more and more pollutants, and as a result, the atmospheric environment is polluted seriously. Thus the progress of human society is at the expense of the environment [
1]. In recent years, areas with polluted air frequently suffer from haze-fog weather conditions in autumn and winter. Especially, in the winter of 2012, a large-scale emergence of haze-fog weather affected the mid-east areas of China, and PM
2.5, which is one of the key pollution factors in the air environment, became a hot topic in China [
2]. As a result the atmospheric environment in China was very harsh, and human health and transportation were seriously affected. The data of the Ministry of Environmental Protection showed that there was large-scale haze-fog pollution in Northeast China, Northwest China, North China, Eastern China and Central China [
3,
4]. The wide range of haze-fog weather triggered a series of chain reactions, including transportation restrictions, flight delays and increased numbers of patients,
etc., and people’s life was severely affected [
5,
6]. In order to protect and improve the living environment and quantitatively analyze the atmospheric environment pollution, new ambient air quality standards were formulated by the Ministry of Environmental Protection [
7]. As a result, the “Air Quality Index” (AQI) was introduced to replace the old “Air Pollution Index” (API), and the “Technical Regulations on Ambient Air Quality Index (Trial) (HJ 633-2012)” [
8] were published to calculate the AQI.
The severe haze-fog pollution situation has attracted serious concern of academic researchers. Numerous studies have been conducted to investigate the composition, sources, and chemical reactions of the haze-fog pollution in China [
9,
10,
11]. Some scholars claimed the haze-fog pollution was usually accompanied with aerosol concentrations in the atmospheric environment, and had significant impacts on the air quality, human health and visibility [
12,
13,
14]. The formation of haze-fog was very closely linked to atmospheric and meteorological conditions [
15,
16]. Zhao
et al. argued that the main source of haze-fog in winter was anthropogenic emissions on a regional scale [
17]. Che
et al. investigated the optical characteristics of the aerosols of haze-fog [
18], and Zhang
et al. analyzed the main chemical components of the aerosols [
19]. Wang
et al. simulated the severe winter of 2013 regional hazes in East Asia and northern China based on simulation models [
20].
In order to deal with the haze-fog pollution, the degree of haze-fog pollution should be known first. In this study the ambient air quality was evaluated to investigate the status of haze-fog. Evaluation of ambient air quality is an important part of any atmospheric ecology studies. The assessment of environmental air quality is the process of quantitative description of the ambient air quality by mathematical methods and models. It can help know the present situation and future tendencies of the ambient air quality [
21]. Thus, it can provide a scientific basis for the planning and management of ambient air quality. Studies on the evaluation of air quality are an important issue, and have attracted the interest of many scholars. The fuzzy comprehensive evaluation theory was applied in air quality assessment according to the national air quality standard [
22]. The level of environmental quality was determined based on the ambient air monitoring data of Dongzhi Country [
23]. Artificial neural networks and decision tree models were applied to evaluate the common Air Quality Index in Thessaloniki, Greece [
24]. The forest air quality in Yichun Town was evaluated based on BP neural networks [
25].
In this study the current situation of haze-fog pollution in China was introduced, and the new ambient air quality standards were analyzed. A comprehensive evaluation model was developed based on an entropy weighting method and nearest neighbor method, and it was applied into the practical problems of air quality in Beijing to analyze the haze-fog pollution status. The entropy weighting method was used to determine the weights of indicators, and the nearest neighbor method was used to evaluate the levels of air quality. Two simulation experiments were implemented. One experiment was with PM2.5 and carried out based on the new Ambient Air Quality Standards (GB 3095-2012); the other experiment was without PM2.5 and carried out based on the old Ambient Air Quality Standards (GB 3095-1996). We compared their results to investigate the importance of PM2.5 and the effects of standards. The situation of haze-fog pollution in Beijing City was then analyzed based on these results.
4. Evaluation Model and Algorithm
For the issue of air quality evaluation, a comprehensive evaluation model based on the entropy weighting method and nearest neighbor method was developed. The entropy weighting method was used to weight the various air quality indicators, and the importance of each indicator was analyzed. The nearest neighbor method was utilized to evaluate the air quality according to the Ambient Air Quality Standards. The algorithm of the evaluation model is shown in
Figure 2.
Then the comprehensive evaluation model was applied to the practical problem of evaluating the air quality in Beijing to analyze the haze-fog pollution status. Because the most important changes of the Ambient Air Quality Standards were the introduction of PM
2.5, we set two simulation experiments, one is with the indicator of PM
2.5, and the other not. The simulation experiment with PM
2.5 was carried out based on the new Ambient Air Quality Standards (GB 3095-2012), and the other experiment without PM
2.5 was based on the old Ambient Air Quality Standards (GB 3095-1996). We compared their results, and analyzed the air quality of Beijing City at the same time. Thus the ambient air quality of Beijing City was analyzed comprehensively, and it is hoped that the results will provide helpful suggestions for the health and life of the people. The study procedures of this paper were as follows:
Step 1: Initialize, and collect the original data of all indicators of air quality;
Step 2: Define the indicators and their weights. The entropy weighting method was used to determine the weights of all indicators, and their importance was analyzed;
Step 3: Construct the evaluation model based on the nearest neighbor method, and it was used to evaluate the air quality of Beijing City;
Step 4: Use the model to evaluate the air quality in two simulation experiments. One experiment was with PM2.5 and carried out based on the new Ambient Air Quality Standards (GB 3095-2012); the other experiment was without PM2.5 and carried out based on the old Ambient Air Quality Standards (GB 3095-1996);
Step 5: Compare the results of the two simulation experiments, and analyze the air quality of Beijing City according to the evaluation results of the model;
Step 6: Draw conclusions, and provide reasonable suggests to decision making according to the research results.
Figure 2.
Evaluation model algorithm.
Figure 2.
Evaluation model algorithm.
6. Conclusions
Haze-fog pollution in China was very severe during autumn and winter in recent years. In order to protect and improve the living environment and analyze the atmospheric environment pollution quantitatively, new ambient air quality standards were issued. A comprehensive evaluation model based on an entropy weighting method and nearest neighbor method was developed according to the new Ambient Air Quality Standards (GB 3095-2012), compared with the old standards (GB 3095-1996). The model was applied into assess the air quality in Beijing in February 2014. The simulation results showed that PM2.5 played an important role in the evaluation process, and could affect the air quality to a large extent. The results based on the new Ambient Air Quality Standards (GB 3095-2012) were more scientific than the old standards (GB 3095-1996). In February 2014 in Beijing there were two continuous periods when the air qualities was severe polluted, that is, the 11th to the 16th and the 20th to the 26th. The air quality in Beijing during less than half a month in February was at Level I, and those of the other dates were at Level II according to the new standards. This was affected by the fireworks during the Spring Festival and adverse weather conditions, and the haze-fog pollution situation in Beijing was still severe.
The haze-fog pollution is heavy in China, and the management and control of haze-fog is very important. The prevention of haze-fog pollution is a systematic project. This requires the environmental protection departments to take the lead, and it also needs social consensus to urge the relevant work. Measures from two aspects are suggested to reduce the haze-fog pollution. One is to reduce the pollution emissions from the sources. We must make efforts to adhere to plans to reduce pollutant emissions. The other is to establish emergency plans for heavy pollution weather. The measures can be taken in advance according to the weather forecast in order to reduce or avoid the occurrence of weather-driven heavy pollution.