Question

You should have noticed that there was a large swath of high concentrations of ozone in the Northern Hemisphere from May to September; why would the highest concentration occur during those months?

Why are there high ozone concentrations over the North Atlantic Ocean during the summer, despite the lack of large NO_x and VOC emissions from the ocean?

Why are we focusing on high levels of ozone in the troposphere in this lab while in Lab 2 (Stratospheric Ozone) we focused on low concentrations of ozone in the stratosphere?

During what months did you observe a large swath of high ozone concentrations in the Southern Hemisphere?

How are the factors that contributed to high ozone concentrations in the Northern Hemisphere different than the factors that contributed to high ozone concentrations in the Southern Hemisphere? Hint: Think about the sources of the precursor chemicals.

Short answers only please.

Answer 1

Ozone is a gas that is naturally present in our atmosphere. Most ozone (about 90%) is found in the stratosphere, which begins about 10.16 kilometers (6.10 miles) above Earth's surface and extends up to about 50 kilometers (31 miles) altitude. Ozone cannot be produced without solar radiation, and emissions of VOCs and NOx typically increase with an increase in temperature. People living in cities with high O3 levels have an increased risk of dying from lung disease. O3 also interferes with photosynthesis, which means it can lead to the reduced agricultural production and the death of forests. Finally, O3 in the troposphere is a greenhouse gas, and has thus contributed to the phenomenon of anthropogenic global warming. Therefore, ozone is “good” in the stratosphere and “bad” down at Earth’s surface As there is so much chlorine in an active form at the end of the polar night (September in Antarctica) the ozone hole can grow to a size larger than the United States.

VOC/NOx ratio

The atmospheric boundary layer cannot be characterized by a single ratio because this ratio varies significantly with location and time of day.

Ambient ratios often exceed by a substantial mount those calculated from emissions inventories.

The goal is to examine data gathered from atmospheric observations to determine if ambient VOC, NOx, and O3 concentrations follow a regular pattern as one moves from an urban or suburban area to a rural area and then to a remote area. By comparing these patterns with those observed in smog-chamber experiments, it may be possible to establish to what degree smog-chamber experiments, and the chemical models based on these experiments can be applied to the atmospheric VOC-NOx-ozone system.

The atmosphere above the Earth is divided into layers (from innermost to outermost: troposphere, stratosphere, mesosphere, thermosphere, and exosphere). We live in the layer of the atmosphere known as the troposphere, which starts at the surface of the Earth and can extend up to 20 kilometers. The next layer is the stratosphere, which is the section found between twenty kilometers and fifty kilometers above the Earth’s surface.

Similar to the troposphere, the stratosphere is comprised almost entirely of nitrogen and oxygen. In contrast to the troposphere, it contains relatively high concentrations of ozone. In fact, the peak ozone concentration occurs between 30 and 35 kilometers above the Earth’s surface, and this is known as the “ozone layer.” Approximately 90% of the ozone in the atmosphere is found in the stratosphere. Keep in mind that even though the concentration of ozone is highest in the stratosphere, ozone still makes up a relatively small percentage of the gases in this layer: Only 0.0003 % of the total amount of gas in the stratosphere is ozone.

Total ozone also varies with season. March and September plots represent the early spring and fall seasons in the Northern and Southern Hemispheres. June and December plots similarly represent the early summer and winter seasons. Total ozone shows a maximum at high latitudes during spring as a result of increased transport of ozone from its source region in the tropics toward the Polar Regions during late fall and winter. This ozone transport is much weaker during the summer and early fall periods and is weaker overall in the Southern Hemisphere.

Seasonal ozone changes is the natural chemical destruction that occurs when daylight is continuous in the summer polar stratosphere, which causes total ozone to decrease gradually toward its lowest values in early fall. This natural seasonal cycle can be observed clearly in the Northern Hemisphere with increasing values in Arctic total ozone during winter, a clear maximum in spring, and decreasing values from summer to fall. In the Antarctic, however, a pronounced minimum in total ozone is observed during spring. The minimum is a consequence of the “ozone hole,” which describes the widespread chemical destruction of ozone by ozone-depleting substances in spring. After spring, these low values disappear from total ozone maps as polar air mixes with lower-latitude air containing much higher ozone values. In the tropics, the total ozone changes through the spring-summer- fall-winter progression of the seasons are much smaller than in the Polar Regions. This is because seasonal changes in both sunlight and ozone transport are smaller in the tropics than in the Polar Regions.