A primary pollutant is an air pollutant emitted directly from a source.
A secondary pollutant is not directly emitted as such, but forms when other pollutants (primary pollutants) react in the atmosphere.
Examples of a secondary pollutant include ozone, which is formed when hydrocarbons (HC) and nitrogen oxides (NOx) combine in the presence of sunlight; NO2, which is formed as NO combines with oxygen in the air; and <em><u>acid rain</u></em>, which is formed when sulfur dioxide or nitrogen oxides react with water.
A construction of the river formed by the floating ice that is accumulated in the rover by the northwards moving direction of the upstream rivers, this significantly reduces the flow of the river and causes the ice dam formation.
Positive reinforcement is the addition of a reinforcing stimulus (giving the dog a treat) following a behavior (rolling over), that makes it more likely that the behavior occurs again.
