Chapter 8 · MCQ Read Mode

Air and Noise Pollution Control

Raising the height of a stack is correctly described as

Ozone in the lower atmosphere is classified as a secondary pollutant because it is

The reason every ambient air quality standard specifies an averaging time is that

The volume ratio in parts per million is preferred for reporting gaseous pollutants in a duct because it is

At 25 °C and one atmosphere, the molar volume used to convert between ppm and μg/m³ is

Particulate matter is always reported as a mass concentration rather than as a volume ratio because it

The principal physical reason for the severity of winter air pollution in the Kathmandu Valley is

Diesel three-wheeler tempos were banned from the Kathmandu Valley in 1999 and replaced by

Carbon monoxide is dangerous at low concentrations principally because it

Sulphur dioxide affects mainly the upper airway while nitrogen dioxide reaches the lower airway because sulphur dioxide is

Sulphur dioxide damages marble and limestone monuments by converting calcium carbonate to

Visibility is reduced most efficiently by particles in the size range

In the hierarchy of air pollution control practices the first option to be considered is

A cyclone of 90 per cent efficiency is followed by a precipitator of 98 per cent efficiency. The overall efficiency is

The chief honest limitation of any air pollution control device is that it

Among the following, the device that genuinely destroys rather than transfers the pollutant is the

Deliberately admitting dilution air ahead of a control device is objectionable because it equipment

Emission concentrations from combustion sources are corrected to a reference oxygen content in order to

Calculations across a combustion or absorption process are conveniently based on the inert flow rate because the inert flow is

A flue gas measured at 1000 m³/h at 0 °C will occupy, at 150 °C and the same pressure, approximately

Ducts carrying dust-laden gas are designed for 15 to 25 m/s because below that velocity

The acid dew point of a flue gas containing sulphur trioxide is

Cooling a flue gas below its acid dew point results in

Selective catalytic reduction of nitrogen oxides with ammonia typically operates in the temperature range

The three-way catalytic converter can control carbon monoxide, hydrocarbons and nitrogen oxides simultaneously only when the engine runs

Unleaded petrol became a legal requirement principally because lead

The terminal settling velocity of a particle in the Stokes regime varies with the particle diameter as

A 10 μm particle of density 2000 kg/m³ settles in air at viscosity 1.8 × 10⁻⁵ Pa·s at approximately

The Cunningham slip correction factor must be applied to particles below about one micrometre because such particles

Stokes' law ceases to be valid when the particle Reynolds number exceeds approximately

For the same dust, the mass median diameter compared with the count median diameter is

The aerodynamic diameter of a particle is defined as the diameter of a sphere that has

PM10 is correctly defined as particulate matter collected with

Deposition of particles in the respiratory tract is at a minimum at a diameter of about

Fine particles of 0.1 to 2 μm have the longest atmospheric residence time because they are removed

The scavenging of particles by raindrops falling beneath a cloud is called

A city that controls only its primary dust emissions typically finds that its PM2.5 concentration

Thermal nitrogen oxide formation becomes significant above a flame temperature of about

Low-NOx burners, flue gas recirculation and staged combustion all reduce nitrogen oxide emission principally by

Isokinetic sampling requires that the sample be drawn into the nozzle at

If a particulate sample is drawn sub-isokinetically, that is too slowly, the measured dust loading will be

Isokinetic sampling is unnecessary when measuring gaseous pollutants because gas molecules

A stack sampling plane should be located

The sample line between the stack and the analyser is heated principally to prevent

The Air Quality Index for a day is taken as

Nitrogen dioxide is measured by chemiluminescence by

The emission rate from a stack is correctly obtained as the concentration multiplied by the volumetric flow rate provided that

A stack of 1.13 m² area carries gas at 12 m/s and 180 °C with a loading of 150 mg/Nm³. The emission rate is approximately

The principal limitation of using a published emission factor in place of a measurement is that the factor

On the Ringelmann scale, a reading of 2 corresponds to an opacity of

Opacity monitoring is a useful compliance screen but is misleading when the plume

A duct cross-section is traversed at the centroids of equal-area segments rather than sampled at a single point because

In the Deutsch-Anderson equation for an electrostatic precipitator, doubling the collecting plate area

A dust of very high electrical resistivity degrades precipitator performance because the collected layer

Several small cyclones operated in parallel are preferred to one large cyclone of the same total capacity because collection efficiency improves as

Raising the inlet velocity of a cyclone improves its collection efficiency but

In an established fabric filter the actual filtration is performed mainly by

The chief advantage of a fabric filter over an electrostatic precipitator is that its performance is

A fabric filter is unsuitable where the flue gas

The venturi scrubber achieves submicron collection principally through

The unique advantage of a wet scrubber over all the dry collectors is that it can

The maximum ground-level concentration downwind of a stack varies with the effective stack height as

The stack exit velocity is conventionally kept above about 1.5 times the wind speed in order to avoid

The plume condition that produces the highest short-term ground-level concentrations is

An atmosphere in which the environmental lapse rate exceeds the dry adiabatic lapse rate of 9.8 °C per kilometre is

Two machines each producing 80 dB operating together produce a level of

If one source is 10 dB louder than another, silencing the quieter source will reduce the combined level by

The sound pressure level from a point source in free field decreases with distance by

A point source gives 90 dB at 10 m. At 40 m the level in free field will be approximately

A-weighting is applied to environmental noise measurements because it

The equivalent continuous sound level Leq is best described as

The day-night level Ldn is computed by adding a penalty to night-time levels of

Noise-induced hearing loss characteristically appears first in the audiogram as a notch at

The occupational noise exposure limit of 85 dB(A) applies to a working day of

A noise barrier beside a road is effective only if it

A line of dense trees planted as a noise barrier typically provides an attenuation of about

According to the mass law, doubling the surface mass of a partition increases its sound transmission loss by about

The Nepali national noise standard for an urban residential area is commonly cited as