QUALITY OF AIR: DAY Vs NIGHT

https://scroll.in/article/807037/going-by-air-pollution-data-early-
morning-exercise-isnt-a-good-idea-in-these-four-metros
Mornings experience the worst air pollution in four Indian cities, according
to an analysis of particulate matter 2.5 data from IndiaSpend’s #Breathe air
quality sensors, analysed from Bengaluru, Chennai, Delhi and Mumbai.
Bengaluru: Best air quality – midnight
The worst air quality was at 7 am, as PM 2.5 concentrations peaked at 61.54
micrograms per cubic metre of air (μg/m3). The air quality improved as the
day wore on, worsening by evening at about 5 pm, reaching a late evening
high at 7 pm (57.60 μg/m3). The best air quality was registered around
midnight, when PM 2.5 levels fell as low to 40.12 μg/m3.
Chennai: Best air quality – 3 pm
The worst air was at 7 am, when PM 2.5 levels (61.54 μg/m3) reached their
peak. Levels began to peak over the night and slide during the day, after 7
am. The best air quality was recorded in the afternoon, at 3 pm, with PM 2.5
levels reaching as low as 20.76 μg/m3.
Delhi: Best air quality – 4 pm
Mornings were the worst time, with PM 2.5 levels reaching as high as 108.16
μg/m3 at 7 am. Air quality gradually improved as the day wore on, registering
the cleanest air at 4 pm (22.84 μg/m3). Pollution levels then picked up
through the night.

Delhi topped the list of the world’s most polluted cities, according to the
World Health Organization.
Mumbai: Best air quality – 5 pm
The worst hour for a Mumbaikar is 8 am, with PM 2.5 levels reaching 48.61
μg/m3; the air started to worsen after 5 am. The best air quality was
registered at 5 pm, when PM 2.5 levels were 22.38 μg/m3.

Outdoor air pollution causes 670,000 deaths annually in India, according to

this 2014 research paper from the Indian Institute of Management-Ahmedabad.
Air pollution has become a global concern with rising air pollution levels,
as outdoor air pollution in cities and rural areas across the world estimated
to cause 3.7 million premature deaths in 2012, according to the World Health
Organization.
Particulate matter, or PM, is the term for particles found in the air,
including dust, dirt, soot, smoke, and liquid droplets. These are classified
according to their diameter. Particles less than 2.5 µm (micrometres) are
called PM 2.5. They are approximately 1/30th the average width of a human
hair. Particles between 2.5 to 10 µm in diameter are called PM 10.

PM 10 and PM 2.5 include inhalable particles that are small enough to

penetrate the thoracic region of the respiratory system. The health effects
of inhalable PM are well documented, caused by exposure over both the short-
term (hours, days) and long-term (months, years). They include: Respiratory
and cardiovascular morbidity such as aggravation of asthma, respiratory
symptoms, and an increase in hospital admissions; and mortality from
cardiovascular and respiratory diseases and from lung cancer.
There is good evidence of the effects of short-term exposure to PM 10 on
respiratory health, but for mortality, and especially as a consequence of
long-term exposure, PM 2.5 is a stronger risk factor than the coarse part
of PM 10.
There is a close relationship between exposure to high concentrations of
small particulates (PM 10 and PM 2.5) and increased mortality and morbidity
from cardiovascular/respiratory diseases and cancer, both daily and over
time, according to the WHO.

ATMOSPHERE:
https://www.nationalgeographic.org/encyclopedia/atmosphere/

https://www.jagranjosh.com/general-knowledge/composition-of-air-
1447673605-1
https://www.openaccessgovernment.org/atmospheric-science-air-pollution-at-
night/110484/

Earth’s atmosphere stretches from the surface of the planet up to as far as

10,000 kilometers (6,214 miles) above. After that, the atmosphere blends
into space. Not all scientists agree where the actual upper boundary of the
atmosphere is, but they can agree that the bulk of the atmosphere is located
close to Earth’s surface—up to a distance of around eight to 15 kilometers
(five to nine miles).
COMPOSITION OF AIR
Nearly all of the Earth's atmosphere is made up of only five gases:
nitrogen, oxygen, water vapor, argon, and carbon dioxide. Several other
compounds also are present.
▪ Nitrogen - 78% - Dilutes oxygen and prevents rapid burning at the
earth's surface. Living things need it to make proteins. Nitrogen
cannot be used directly from the air. The Nitrogen Cycle is nature's
way of supplying the needed nitrogen for living things. Nitrogen is
very important for plant’s survival. They cannot take nitrogen
directly from the air. Bacteria that live in the soil and roots of
some plants take nitrogen from the air and change its form so that
plants can use it.
▪ Oxygen - 21% - Used by all living things. Essential for respiration.
It is necessary for combustion or burning. Oxygen is the second most
plentiful gas in the air. Humans and animals take oxygen from the
air. Green plants produce oxygen during photosynthesis.
 ▪ Argon - 0.9% - Used in light bulbs. Derived from the decay of
potassium-40 in the Earth's crust.
▪ Carbon Dioxide - 0.03% - Carbon dioxide is another important gas.
Green plants use carbon dioxide to make their food and release
oxygen. Humans or animals release carbon dioxide. The amount of
carbon dioxide released by humans or animals seems to be equal to
the amount used by the plants which make a perfect balance. Acts as
a blanket and prevents the escape of heat into outer space.
Scientists are afraid that the burning of fossil fuels such as coal
and oil are adding more carbon dioxide to the atmosphere.
▪ Water Vapor - 0.0 to 4.0% - Essential for life processes. Also
prevents heat loss from the earth.
▪ Trace gases - gases found only in very small amounts. They include
neon, helium, krypton, and xenon. They arise from natural phenomena
such as volcanic eruptions, lightning strikes and forest fires.
Others are photosynthesis, animal excrements, termites, rice
paddies, and wetlands.

This is composition of air in percent by volume, at sea level at 15°C and

101325 Pa

Nitrogen N2 78.084%

Oxygen O2 20.947%

Argon Ar 0.934%

Carbon Dioxide CO2 0.033%

Neon Ne 18.2 parts per million

Helium He 5.2 parts per million

Krypton Kr 1.1 parts per million

Sulphur dioxide SO2 1.0 parts per million

Methane CH4 2.0 parts per million

Hydrogen H2 0.5 parts per million

Nitrous Oxide N2O 0.5 parts per million

Xenon Xe 0.09 parts per million

Ozone O3 0.07 parts per million

Nitrogen dioxide NO2 0.02 parts per million

Iodine I2 0.01 parts per million

Carbon monoxide CO trace

Ammonia NH3 trace

LAYERS
The atmosphere is divided into five different layers, based on temperature.
The layer closest to Earth’s surface is the troposphere, reaching from about
seven and 15 kilometers (five
to 10 miles) from the surface.
The troposphere is thickest at
the equator, and much thinner
at the North and South Poles.
The majority of the mass of the
entire atmosphere is contained
in the troposphere — between
approximately 75 and 80
percent. Most of the water
vapor in the atmosphere, along
with dust and ash particles,
are found in the troposphere —
explaining why most of Earth’s
clouds are located in this
layer. Temperatures in the
troposphere decrease with
altitude. Almost all the
weather phenomena like rainfall, fog and hailstorm occur in this layer.
The stratosphere is the next layer up from Earth’s surface. It reaches from
the top of the troposphere, which is called the tropopause, to an altitude
of approximately 50 kilometers (30 miles). Temperatures in the stratosphere
increase with altitude. A high concentration of ozone, a molecule composed
of three atoms of oxygen, makes up the ozone layer of the stratosphere. This
ozone absorbs some of the incoming solar radiation, shielding life on Earth
from potentially harmful ultraviolet (UV) light, and is responsible for the
temperature increase in altitude. This layer is almost free from clouds and
associated weather phenomenon, making conditions most ideal for flying
aeroplanes.
The top of the stratosphere is called the stratopause. Above that is the
mesosphere, which reaches as far as about 85 kilometers (53 miles) above
Earth’s surface. Temperatures decrease in the mesosphere with altitude. In
fact, the coldest temperatures in the atmosphere are near the top of the
mesosphere—about -90°C (-130°F). The atmosphere is thin here, but still
thick enough so that meteors will burn up as they pass through the
mesosphere—creating what we see as “shooting stars.” The upper boundary of
the mesosphere is called the mesopause.

The thermosphere is located above the mesopause and reaches out to around
600 kilometers (372 miles). Not much is known about the thermosphere except
that temperatures increase with altitude. Solar radiation makes the upper
regions of the thermosphere very hot, reaching temperatures as high as
2,000°C (3,600°F). This layer helps in radio transmission. In fact, radio
waves transmitted from the earth are reflected back to the earth by this
layer.

The uppermost layer, that blends with what is considered to be outer space,
is the exosphere. The pull of Earth’s gravity is so small here that molecules
of gas escape into outer space. This layer has very thin air. Light gases
like helium and hydrogen float into the space from here.
WEATHER AND CLIMATE
Weather is the mix of events that happen each day in our atmosphere including
temperature, rainfall and humidity. Weather is not the same everywhere.
Climate refers to the average weather condition of a place for a longer
period of time. The temperature is the degree of hotness and coldness of the
air. The temperature of the atmosphere changes not only between day and
night but also from season to season. Insolation is the incoming solar
energy intercepted by the earth which influences the distribution of
temperature. The amount of insolation decreases from the equator towards the
poles.
AIR PRESSURE
The pressure exerted by the weight of air on the earth’s surface is called
air pressure. The air pressure is highest at sea level and decreases with
height. Horizontally the distribution of air pressure is influenced by
temperature of air at a given place. Low–pressure areas where temperature
is high the air gets heated and rises. It is associated with cloudy skies
and wet weather. High pressure is associated with clear and sunny skies
which mean areas having lower temperature, the air is cold. Heavy air sinks
and creates a high-pressure area. The air always moves from high pressure
areas to low-pressure areas.
Atmospheric stability defines the tendency for vertical motion in the
atmosphere. Stability is a classification technique. A stable atmosphere
will suppress or inhibit vertical motion and unstable atmosphere will promote
it, and a neutral atmosphere is somewhere in between. Stability is one of
the first steps in understanding where something released into the atmosphere
might go. In other words, understanding atmospheric stability is fundamental
to understanding air pollution.

Day versus night

Stable boundary layers can occur at any time, but they are most frequent at
night. During the day, the Sun heats the ground, the ground heats the air,
and the warm air rises. This process of convection causes a constant
overturning and promotes vertical mixing. A pollutant released near the
surface during the day has a higher probability of moving higher into the
atmosphere. Higher into the atmosphere means a lower chance for immediate
human or environmental exposure (It is important to note that there are
longer-term impacts of daytime pollutant releases, but they are outside the
scope of this article).

When the Sun goes down, this relationship changes. When the Sunsets, the
loss of solar radiation promotes cooling of the ground surface. This promotes
an air–surface temperature difference at the ground. This temperature
difference defines the intensity of the air stability. It is night half of
the time annually. More stable air means less potential for vertical mixing
and more potential for horizontal spread.

In this way, stability in combination with wind speed and direction can be
a valuable tool for determining where something will disperse and ultimately
end up when it is released into the atmosphere.

OZONE IN ATMOSPHERE:
https://ozone.meteo.be/research-themes/ozone/introduction

https://www.treehugger.com/the-good-and-bad-of-ozone-1204081

Ozone (O(3)) is present both in the troposphere and the stratosphere.

Troposphere O(3) is predominantly produced by photochemical reactions
involving precursors generated by natural processes and to a much larger
extent by man's activities.

There is evidence for a trend towards

increasing tropospheric O(3) concentrations.
However, tropospheric O(3) is known to
account for only 10% of the vertical O(3)
column above the earth's surface. The
stratosphere accounts for an additional 90%
of the O(3) column.

There is evidence to suggest that there are

losses in the stratospheric O(3) due to the
updraft of O(3) destroying pollutants
generated by both natural processes and by
human activity. Such a loss in stratospheric O(3) can
result in alterations of incidence in the ultraviolet (UV) radiation to the
earth's surface.

Tropospheric O(3) is known to be highly phytotoxic. Appropriate exposures

to O(3) can result in both acute (symptomatic) and chronic (changes in
growth, yield or productivity and quality) effects. Chronic effects are of
great concern in terms of both crops and forests.

Stratospheric ozone

Stratospheric ozone is formed when solar energetic ultraviolet (UV)

radiation dissociates molecules of oxygen, O 2, into separate oxygen atoms.
Free oxygen atoms can recombine to form oxygen molecules but if a free oxygen
atom collides with an oxygen molecule, it joins up, forming ozone.

Ozone molecules can also be decomposed by UV radiation into a free atom and
an oxygen molecule. Ozone is thus continuously created and destroyed in the
stratosphere by UV radiation coming from the sun.

The stratospheric region with the highest concentration of ozone, between

about 15 and 35 km altitude, is known as the ozone layer.

Stratospheric ozone ("the good ozone"), is beneficial for life on Earth

because it absorbs the harmful UV radiation from the Sun.

In the absence of the ozone layer, the higher UV radiation from the Sun
would impact many living organisms on Earth, causing sun burn, skin cancer,
eye diseases like cataract, but also plankton damage in the oceans, smaller
crop yields, biodiversity disappearance, etc.

The ozone creation/destruction processes in the stratosphere are normally

(naturally) balanced, so that the total amount of ozone in the atmosphere
should remain more or less constant.

In the 1970s, it was discovered that gases containing chlorine, nitrogen and
bromine atoms released by human activities could cause stratospheric ozone
depletion. In these reactions, those atoms acts as catalysts, i.e. they
facilitate ozone loss reactions without being consumed themselves. As such,
for example, one individual chlorine atom in the stratosphere can destroy
during its lifetime about 100.000 ozone molecules.

In addition to the gases emitted by human activities, factors such as changes

in solar radiation and the formation of stratospheric aerosol particles
after explosive volcanic eruptions also influence the ozone layer.

Tropospheric ozone

Most of the tropospheric ozone formation occurs when nitrogen oxides (NOx),
carbon monoxide (CO) and volatile organic compounds (VOCs), react in the
atmosphere in the presence of UV radiation.

Tropospheric ozone in excess of the natural amounts of ozone, is considered

as "the bad ozone". High ozone levels in the boundary layer (from the surface
to 100-3000m) can have adverse impacts on human and animal health (e.g.
respiratory problems) and on the vegetation.

The man-made ozone that forms in the troposphere is extremely toxic and
corrosive. People who inhale ozone during repeated exposure may permanently
damage their lungs or suffer from respiratory infections. Ozone exposure may
reduce lung function or aggravate existing respiratory conditions such as
asthma, emphysema or bronchitis. Ozone may also cause chest pain, coughing,
throat irritation or congestion.
Finally, it should also be noted that ozone in the upper troposphere is an
important absorber of infrared (terrestrial) radiation, and therefore acts
as a greenhouse gas.

Tropospheric ozone is also the main source of the OH free radical, the
primary oxidant in the atmosphere, responsible for removing many compounds
(including atmospheric pollutants) from tropospheric air. OH is therefore
called the “detergent of the atmosphere”.