Identify the non-weightless pollutant in environmental engineering Among the listed pollutants, which one is not “weightless” (i.e., it consists of material particles with mass rather than energy or fields)?

Introduction / Context:
Pollutants encountered in environmental engineering can be broadly grouped into two types: those that are material (having mass, like particles or chemicals) and those that are essentially forms of energy (sound, heat, or ionising radiation). Understanding this distinction helps engineers select appropriate monitoring methods and control technologies, because equipment designed to capture matter behaves very differently from measures that attenuate energy.

Given Data / Assumptions:

• The term “weightless pollutant” here refers to energy-based pollutants lacking rest mass in the way particulate matter does.
• Options mix particulate and energy examples.
• Engineering focus is on common plant and urban environments.

Concept / Approach:
Suspended particulate matter (SPM) consists of physical particles (dust, smoke, soot, aerosols) and therefore has mass and “weight.” By contrast, thermal pollution describes excess heat released to the environment; radioactive rays refer to emitted radiation (alpha, beta, gamma) as an energy hazard; and noise pollution is unwanted sound energy. These energy phenomena are not captured by gravimetric samplers in the same way as SPM, and they require different mitigation strategies (cooling systems, shielding, or acoustic controls).

Step-by-Step Solution:

Verification / Alternative check:
Standard air quality methods: gravimetric PM samplers weigh captured SPM; sound is measured in decibels; thermal loads are measured as temperature or heat flux; radiation is measured via dose or count rate. Different metrology confirms the classification.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing radioactive contamination (material radionuclides, which have mass) with radiation (energy). Here, “radioactive rays” denotes the energy aspect.

Final Answer:
SPM