Is rain with a pH less than 7 necessarily acid rain? How is acid rain formed?

Acid rain is mainly caused by burning large amounts of coal with high sulfur content. Most of it is sulfuric acid rain, and less is nitric acid rain. In addition, exhaust gas emitted by various motor vehicles is also an important cause of acid rain. Some areas in my country have become acid rain-prone areas, and the scope and degree of acid rain pollution have attracted close attention. Is rain with a pH less than 7 necessarily acid rain? Do you know if this is the case?

Contents of this article

1. Is rain with a pH less than 7 necessarily acid rain?

2. How is acid rain formed?

3. The main components of acid rain

4. What are the specific aspects of the harm of acid rain?

Is rain with a pH less than 7 necessarily acid rain?

Acid rain refers to rain, snow, fog, hail and other atmospheric precipitation with a pH value less than 5.6, so a pH less than 7 is not necessarily acid rain. Acid rain is wet deposition in acidic deposition, which can be divided into two categories: "wet deposition" and "dry deposition". The former refers to all gaseous pollutants or particulate pollutants that fall to the ground with precipitation forms such as rain, snow, fog or hail, while the latter refers to acidic substances carried by dust falling from the sky on days when it is not raining. Acid rain is divided into nitric acid rain and sulfuric acid rain.

During the formation and falling process, rain and snow absorb and dissolve sulfur dioxide, nitrogen oxides and other substances in the air, forming acidic precipitation with a pH value below 5.6. Acid rain is mainly caused by the human emission of large amounts of acidic substances into the atmosphere. Acid rain in my country is mainly caused by the burning of large amounts of coal with high sulfur content, mostly sulfuric acid rain and less nitric acid rain. In addition, exhaust gas emitted by various motor vehicles is also an important cause of acid rain. Some areas in my country have become acid rain-prone areas, and the scope and degree of acid rain pollution have attracted close attention.

How is acid rain formed?

1. Emission and conversion conditions of acidic pollutants. Generally speaking, the more serious the pollution in a certain place, the higher the concentration of sulfate ions in the precipitation, resulting in a lower pH value.

2. Ammonia in the atmosphere is very important for the formation of acid rain. Due to its water solubility, it can react with the acid in acid aerosol or rainwater, neutralizing it and reducing the acidity.

3. The impact of particulate matter on acid rain. Particulate matter has two effects on the formation of acid rain. First, the catalytic metals contained in it promote the oxidation of sulfur dioxide into acid; second, it neutralizes the acid. However, if the particulate matter itself is acidic, it cannot play a neutralizing role and will become one of the sources of acid.

4. Influence of weather conditions: If meteorological conditions and terrain are conducive to the diffusion of pollutants, the concentration of pollutants in the atmosphere will decrease and acid rain will weaken. Otherwise, it will worsen (such as inversion phenomenon).

The main components of acid rain

The main components of acid rain are sulfuric acid and nitric acid. Acid rain is divided into two types: sulfuric acid type and nitric acid type. In my country, sulfuric acid rain is more common and nitric acid rain is less common.

1. Formation of sulfuric acid type acid rain: It is mostly caused by the combustion of fossil fuels. The combustion of sulfur-containing coal produces sulfur dioxide, which reacts with water to produce sulfurous acid. Sulphurous acid can be oxidized into sulfuric acid in the air.

2. Formation of nitric acid rain: During thunderstorms and lightning, a small amount of nitrogen dioxide is often produced in the atmosphere. During lightning, nitrogen combines with oxygen to form nitric oxide. Nitric oxide is structurally unstable and is oxidized into nitrogen dioxide in the air. Nitrogen dioxide reacts with water to form nitric acid.

What are the specific hazards of acid rain?

1. Corrosion on the outer surfaces of various materials such as buildings, roads and bridges;

2. Accelerate the corrosion of rainwater pipe system or sewage pipe;

3. Cause soil acidification and soil compaction, and affect the structure of soil microbial communities;

4. Affect underground diving and surface water quality;

5. Harm to human and animal health;

6. Comprehensively affect plant growth and environmental ecology.