In recent years, frequent haze in the north has brought fine particulate matter (PM2.5) into the public eye and attracted attention. With the continuous increase in governance efforts, the PM2.5 concentration in our province has been decreasing year after year and reaching the standard, making "Guangdong Blue" increasingly the norm. In contrast, another lesser known pollutant, ozone (O), is increasingly becoming an important factor affecting the proportion of excellent days (AQl compliance rate). According to the air quality data released by the Provincial Department of Ecology and Environment for the first five months of this year, ozone, as the primary pollutant in the province, accounts for 39.9%
Where does near earth ozone come from?
Ozone is a gas with strong oxidizing properties. More than 90% of the ozone in the atmosphere exists in the upper atmosphere or stratosphere, at a distance of 10-50 kilometers from the ground. This ozone can absorb ultraviolet radiation and protect humans from the harm of ultraviolet radiation. The accumulation of high concentrations of ozone near the ground will reduce atmospheric visibility, lead to greenhouse effect, and may also cause damage to human health.
What are the hazards of ozone?
Ye Daiqi, Dean of the School of Environment and Energy at South China University of Technology, explained that high concentrations of ozone can irritate the eyes, reducing visual sensitivity and vision. It can also cause changes in lung function and even damage to lung tissue, especially for patients with bronchitis, who will suffer significant damage when exposed to ozone.
It is understood that long-term inhalation of ozone may cause tissue hypoxia, damage thyroid function, bone calcification, destroy vitamin E in the skin, cause wrinkles, black spots, etc., accelerate human aging, and even lead to death in severe exposure. Because the production of ozone occurs during the growing season of most plants, an increase in ozone concentration can cause damage to plant leaves, leading to reduced crop yields, decreased forest productivity, and so on.
After ozone accumulates to a certain level, it may also form photochemical smog, which is related to the Los Angeles photochemical smog event in the United States and the London smog event in the United Kingdom.
Where does ozone come from?
The person in charge of the Atmospheric Environment Management Department of the Guangdong Provincial Department of Ecology and Environment introduced that ozone near the ground is mainly generated by photochemical reactions of volatile organic compounds (VOCs) and nitrogen oxides (NOx) in the atmospheric environment under sunlight. Ozone has become the primary pollutant in the province
In recent years, the overall ozone concentration in China has increased to varying degrees compared to the same period last year. Among them, the assessed ozone concentrations in the Pearl River Delta, Beijing Tianjin Hebei, and Yangtze River Delta regions have shown a fluctuating upward trend. Currently, the ozone pollution level in the Pearl River Delta is better than that in the Beijing Tianjin Hebei and Yangtze River Delta regions. From the perspective of Guangdong Province,
Throughout the province and the Pearl River Delta region,
The evaluation concentration of ozone is still at a low and controllable level,
But they all show a fluctuating upward trend.
Observation data from the national air monitoring network shows
From 2014 to 2018, the ozone levels in the province and the Pearl River Delta increased by 5.5% and 5.1% respectively, with an average annual increase of 2 micrograms per cubic meter. Among them, the 90th percentile concentration of the 8-hour mean of ozone in Guangdong Province in 2018 was 154 micrograms per cubic meter, an increase of 0.7% compared to 2017; The Pearl River Delta region has a concentration of 164 micrograms per cubic meter, exceeding the second level standard of 160 micrograms per cubic meter for the 8-hour average concentration limit of ozone in China.
Ozone has become an important factor affecting the AQI compliance rate in our province. In 2018, the proportion of ozone as the primary pollutant in the province reached 59.6%. ”The head of the Provincial Department of Ecology and Environment stated that the ozone concentration in some cities has been consistently high, and the average concentration in ozone regions has not yet shown a downward trend. Previously, the air quality data released by the Provincial Department of Ecology and Environment from January to May 2019 showed that the average concentration of PM2.5 in the province continued to decline, reaching 27 micrograms per cubic meter. Ozone, as the primary pollutant in the province, accounted for 39.9%, higher than PM2.5's 30.6%.
As summer approaches, the sunlight required for ozone formation will become more concentrated under favorable weather conditions. Ye Daiqi stated that with sufficient sunlight and higher temperatures, ozone pollution may become more severe.
There are many types and complex sources of VOCs, making it difficult to control them except for weather conditions. VOCs and NOx are also essential conditions for ozone formation. Professor level senior engineer Zhong Liuju from Guangdong Environmental Protection Engineering Vocational College once made a vivid analogy, similar to treating gout, which manifests as high uric acid. To reduce high uric acid, one should eat less seafood and drink less beer. Ozone is equivalent to gout, high uric acid is equivalent to photochemical reactions, and seafood beer is the focus of treatment, namely "VOCs, NOx". In the view of Qu Yubo, Deputy Director of the Provincial Environmental Monitoring Center, compared to NOx, "VOCs are the difficulty and key to ozone control work. ”He further explained that NOx mainly comes from emissions from motor vehicles, power plants, coal-fired boilers, and other sources. After governance, the national NOx emissions have been decreasing year by year since 2011. VOCs mainly come from emissions from motor vehicles, petrochemical industry, and organic solvent volatilization. There are many types of VOCs, including hundreds of organic compounds such as formaldehyde, benzene, xylene, and various aromatic hydrocarbons. The sources are complex and the research is difficult.
The scientific understanding of atmospheric VOCs is still far from meeting the management and decision-making needs for improving atmospheric environmental quality. ”Qu Yubo believes that there is still a lack of research on the status of atmospheric VOCs pollution at the * * level, especially the lack of a systematic VOCs emission source inventory and source component spectrum library, as well as a lack of VOCs total control technology methods based on environmental quality objectives. VOCs are volatile, and every process from raw material storage to production is accompanied by emissions. Therefore, targeted measures must be taken to control emissions at all stages of the entire process. ”Qu Yubo said that there is currently a lack of research on integrated management of "emission control", and enterprises and management departments lack sufficient experience for specific pollution source control and governance work, which has become a bottleneck problem in controlling VOCs emissions. In addition, there are also issues such as insufficient monitoring capabilities, incomplete governance measures and standards.
Qu Yubo pointed out that VOCs monitoring is the foundation. Although there are various online measurement technologies such as chromatography, mass spectrometry, and spectroscopy, and a fixed pollution source VOCs online monitoring system has been established, the online monitoring methods are still not perfect in terms of quality control and quality management system standards and specifications. Qu Yubo introduced that in practice, the dynamic monitoring of VOCs emissions and chemical components is still mainly based on "manual sampling+offline analysis" in most areas, and the monitoring frequency and timeliness of monitoring results are obviously insufficient, which cannot reflect the changes in gas concentration in a timely manner. Qu Yubo stated that multiple relevant regulations, policies, and standards have been successively introduced, covering most key industries and fields, promoting the legal and evidence-based reduction of VOCs emissions. However, due to the weak research foundation and lack of basic data in the past, the existing VOCs emission standards are still incomplete, and some emission standards for key industries have not yet been approved, resulting in slow progress in establishing the emission standard system and restricting the overall promotion of VOCs governance work.
VOCs online monitoring technology is the future trend
At the Green Service Center for Redwood Industry in Guicheng, Foshan, workers are processing furniture in container like compartments while painting, drying, polishing, and waxing. By sharing devices, the processes that generate pollution can be centrally managed, "said Chen Deqiu, director of the Environmental Protection Office of Guicheng Street in Nanhai District. The exhaust gas is purified through water curtain cabinets, activated carbon filtration and adsorption boxes, and discharged, reducing atmospheric VOCs emissions by about 20 tons per year.
In the polishing room of the Redwood Industry Green Service Center, technicians are polishing the redwood furniture after completing the painting process. It is reported that Guangdong is accelerating the control of VOCs emissions in key industries such as industrial painting, printing, shoemaking, furniture manufacturing, etc., and actively exploring market-oriented mechanisms for ecological environment. In Foshan, relying on the "one certificate" management, Shunde District has taken the lead in promoting VOCs trading pilot projects. At the same time, by increasing efforts to control emissions from mobile sources, utilizing technology such as motor vehicle exhaust detection and supervision platforms, remote sensing monitoring, and black smoke vehicle capture to strengthen in use emission management. Starting from July 1st, Guangdong officially implemented the National VI emission standard for light-duty vehicles. Compared with the National V standard, nitrogen oxides (NOx) decreased by 42%, and total hydrocarbons (THC) and non methane hydrocarbons (NMHC) decreased by 50% respectively. In terms of VOCs monitoring technology, Qu Yubo stated that compared to offline monitoring technology, online monitoring technology has higher time resolution and avoids interference caused by sample storage and transportation. It should become the main direction for the future development of VOCs analysis and detection. The person in charge of Guangdong Academy of Environmental Sciences also mentioned that there are significant differences in the mechanisms and characteristics of ozone formation in different regions, and further research and policy implementation are still needed. Ozone pollution is mobile, and the downwind areas of cities are prone to peak ozone levels in summer and autumn. Therefore, there is a need for regional awareness of prevention and control, and coordinated control of NOx and VOCs.
expert opinion
Ye Daiqi, Dean of the School of Environment and Energy at South China University of Technology: Implement zoning control and develop targeted prevention and control routes. Guangdong has always attached great importance to the prevention and control of air pollutants. After years of efforts, a pollutant in the the Pearl River Delta has been effectively controlled. In recent years, Guangdong Province has successively released the "2017 Pearl River Delta Ozone Pollution Prevention and Control Special Action Plan", which puts forward requirements for ozone pollution prevention and control. However, overall, due to Guangdong being a region that emits a large amount of ozone precursors and favorable climate conditions for ozone production, the prevention and control of ozone pollution face significant challenges. In terms of ozone pollution control, ozone is a secondary pollutant generated through photochemical reactions, with complex reaction mechanisms and difficult control. In recent years, various regions in China have begun to control the emissions of their precursor volatile organic compounds, but effective prevention and control policies and management systems have not yet been established. Ye Daiqi suggested that systematic scientific research should be carried out to solve the problem of ozone pollution, the chemical mechanisms of ozone generation, and the cross regional spread of pollution, providing directional guidance for policy-making. Improve relevant laws and regulations, and enhance the control of the ozone precursor industry. Develop a scientifically reasonable VOCs and NOx coordinated control plan, and implement coordinated prevention and control of ozone and PM2.5. Drawing on the experience of the United States, implement ozone pollution zoning control in China, establish a method for ozone control zoning in China, divide ozone control zones, comprehensively consider the characteristics of different regions, and propose ozone prevention and control routes for different regions and precursors.