Volcanic eruptions and emissions from vegetation are the natural causes of which phenomenon

Acid rain

The volcanic eruption is a natural phenomena that results in the liberation of the lava from the heap of the earth along with the gases. The volcanic eruption causes major damages to the vegetation lying above the erupted crater of the volcano. This results in the immense release of gases such as carbon dioxide, carbon monoxide, sulfur dioxide, hydrogen chloride, hydrogen fluoride, methane and ammonia all these gases are major pollutants of the air. These gases reacts with water vapor in the atmosphere and condense in the form of acid rain.  

relative humidity, temperature and dew point -- are bound together in the mathematical relationship below. relative humidity changes when temperatures change. because warm air can hold more water vapor than cool air, relative humidity falls when the temperature rises if no moisture is added to the air. so i would say a

the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.