Ground-Level Ozone

Ground level ozone (GLO) is a highly irritating gas that forms immediately above the surface of the earth. It is a pollutant gas and falls in the “secondary” category as it develops through the combination of two primary pollutants in the presence of sunlight and still air. The two agents of pollution, in this case, are volatile organic compounds (VOCs) and nitrogen oxides (NOx) which are unstable. This gas is different from the atmospheric ozone which is stable and prevents the harmful radiations of the sun from reaching the surface of the earth. VOCs and NOx emanate from both natural sources and human activities. About ninety-five percent of nitrogen oxides from human activities are from burning fossil fuels such as oil, gasoline, and coal in homes, power plants, industries, and apartments. VOCs that arise as a result of human activities are mainly from the marketing and combustion of gasoline, burning of wood in residential areas, oil and gas extraction in upstream, and evaporation of liquid fuels and solvents. This means that humans contribute a huge chunk of the occurrence of ground-level ozone because every aspect of life nowadays depends heavily on the combustion of fossil fuels. When NOx and VOCs react in the presence of sunlight, the most noticeable effect is smog, which has been a characteristic of many urban cities in the recent past. The factors influencing the concentration of ozone are VOCs and NOx concentration, the intensity of solar radiation, and the ratio of NOx to VOCs. Accumulation of GLO occurs when the sea breezes cause air circulation over the ground or in areas that have air inversion due to temperature trap atmospheric compounds that produce smog. Ground level ozone has severe health impacts with the primary concern being its effect on the respiratory system. When a person inhales the contaminated air, it causes blockage in the lungs that hinder the pick-up of oxygen by the cells hence jeopardizing the functions of these organs. This effect has the highest impact on those who suffer from respiratory disorders such as asthma. It can trigger new attacks or aggravate the existing asthma condition to fatal levels. The reason behind this is that ground-level ozone interferes with air quality, which is essential for breathing. Other states that have been linked to GLO are pre-mature mortality and a wide range of morbidity like hospital admissions ( Pui et al., 2014) . Besides having adverse impacts on human health, ground-level ozone has a significant effect on crops and vegetation as it injures flowers, reduces productivity, and causes forest decline in forested areas. The trend of gaseous emissions from vehicles has decreased significantly over time and continues to decline. In a study conducted in Atlanta, the rate of emissions of VOCs, NOx, and CO reduced considerably by 54%, 40%, and 60% respectively ( Vijayaraghavan et al., 2014) . In this sense, it is possible to infer that the particles that increase the level of GLO are decreasing thus making the trend of its occurrences to be declining as shown in Figure 1. One of the measures that have caused this decline is the existence of strict emission rules and the extinction of the vehicles that previously emitted many gases and the introduction of cars that are catalytic to ensure maximum combustion of gases. The other strategy is the regulation of the age a vehicle can be on the road after manufacture. This provides that the old cars, which are responsible for the emissions, are phased out immediately after they begin to produce harmful gases. Right now, the levels of smog occurrences are increasing as the measure of ground-level ozone hit higher records than in preceding years. Significant cases of this type of pollution have been recorded in Los Angeles, California. Due to its vast cities and oil exploration in the downtown, this city stands to be the most polluted in the United States. Its worst levels were in 2013 when the levels of PM 2.5 were 18, against a set annual standard of 20 and 12.4 micrograms per cubic meter or below in the World Health Organization and US standards respectively. But, what is astonishing is that L.A. cannot be compared to all the seventy-four cities of China. If it were in China, it would be the cleanest. China has recorded levels of as high as 600 micrograms per square meter of air of particulate matter in Beijing, with other stations reaching up to 900 ( Xue et al., 2014) . This resonates with an incident in 1952 in London which is dubbed “The Great Smog of London.” Although not measured, this event made humans wake up to the reality of the dangerous effects of air pollution as it caused the deaths of more than twelve thousand people. On that day, a cold layer of air stagnated under a layer of warm air, causing temperature inversion which caused the smog to be denser to disperse. The means of obtaining the measure of the level of GLO and any other pollutant requires environmental sampling of air. The main component that the quality of air entails is the particulate matter (PM 2.5 and 10) whose levels need to be frequently monitored (Lin et al., 2014). To achieve this, the process begins with the collection of samples of air that is suspected to contain harmful components and then analyzing them in the laboratory to obtain results and then interpret the data. One way of collecting the samples is by using filter media and plug foams to analyze the chemicals that are toxic to humans and the environment. For the VOCs that contribute to the formation of smog, a canister can be used. Some of the compounds of interest are those of benzene, which is released into the atmosphere by burning motor vehicle engines. Another medium for collecting the samples is the passive diffusion tubes, which do not require pumping and can be used successfully to sample nitrogen oxides and benzene. When the smog or GLO is already formed, the total suspended particles (TSP) are pumped through a filter medium made of paper for solid particles, and sorbent for gases (Lin et al., 2014). Many factors can influence the choice of a location to use for data collection or air monitoring. One of these is the use of data collected, which defines the need for the information obtained from the stations. A monitoring site can be used to convey data that is used to map the level and effects of pollution from one source. For instance, one may consider the contamination that is coming from an area with oil rigs or energy generation plants such as a nuclear plant. If this is the case, then the location will be such that the site will be a definitive collection of samples with the notion that they represent the pollution from either the rigs or the nuclear plants. Another condition can be that the data collected acts as a representative of a more extensive area such as a city or a state (Lin et al., 2014). The information received from the station would be used to conclude that it represents the geographical boundary of interest. The two cases require different designs of data collection methods and strategies as there is the question of the time frame representation that the data provides. Mostly, the location is supposed to be in a place where people live, work or play. With that in mind, there are various means of identifying a sampling site due to the factors of interest that guide this selection. First, the site has to be away from obstacles that can restrict the flow of air in the vicinity of the inlet. This means that places that have trees, walls, and buildings will interfere with the results and thus should be avoided. The site should be in a clear sky, away from overhanging foliage. Secondly, the site has to be away from areas that are prone to chemical instability and interference. Such areas are the roadside where vehicles continuously deposit chemicals that can exaggerate the levels of GLO in the device used for sampling. Thus, unless the effect of emissions from automobiles is the interest of the sample, the roadside should be avoided, and this also applies to power generation plants. The location of the devices has to be close to the nearby source of energy while taking into consideration the safety of the passers-by when connecting the cables (Lin et al., 2014). Security is also another critical element in location as it has to be away from interference by the people. This can be enhanced by putting a fence around the area or using lids and gauges. During sampling, I would employ a continuous sampling method to analyze the air quality. This method employs the use of automated data collection and analysis during the entire period of the day at given intervals. Compared to the grab method which only provides the instantaneous condition, the continuous approach offers flexibility to the changes taking place in the environment. During the day, the temperatures can, and this can affect the occurrence of ground-level ozone. Thus, this method automatically records the level on every occasion, and it is not a must for someone to be there physically. This method also possible to sample a representation 

In conclusion, ground-level ozone is a nuisance that has severe effects on both humans and the environment and thus has to be continuously monitored. The cases of smog have been on the rise in other parts of the world especially in the oil-producing regions and the highly urban ones, although the American areas have shown declines in the concentrations. Part of this is because of human activities which continue to choke the earth. Thus, a lot of attention should be given to the occurrences and regulations be set to fight air pollution. 

References  

Lin, K., Yu, T., & Chang, L. (2014). Establishment of a structural equation model for ground-level ozone: a case study at an urban roadside site. Environmental Monitoring And Assessment, 186(12), 8317-8328. doi:10.1007/s10661-014-4005-1 

Pui, D. Y., Chen, S. C., & Zuo, Z. (2014). PM 2.5 in China: Measurements, sources, visibility and health effects, and mitigation.  Particuology ,  13 , 1-26. 

Vijayaraghavan, K., DenBleyker, A., Ma, L., Lindhjem, C., & Yarwood, G. (2014). Trends in on-road vehicle emissions and ambient air quality in Atlanta, Georgia, USA, from the late 1990s through 2009.  Journal of the Air & Waste Management Association ,  64 (7), 808-816. 

Xue, L. K., Wang, T., Gao, J., Ding, A. J., Zhou, X. H., Blake, D. R., ... & Zhang, Q. Z. (2014). Ground-level ozone in four Chinese cities: precursors, regional transport and heterogeneous processes. Atmospheric Chemistry and Physics, 14(23), 13175-13188.