Tropospheric Chemistry - Precipitation Flashcards

General concepts, chemical reactions, and mathematical models regarding the production of nitric and sulphuric acid in the troposphere based on Chapter 5 of vanLoon & Duffy.

What is the term for the process in which chemical species are removed from the atmosphere during a precipitation event?

Rainout

According to the lecture, what was the $CO_2$ concentration in 2004, and what is the suggested pH of unpolluted rain as a result?

$378\,ppm$ in 2004, resulting in a suggested pH of $5.7$ for unpolluted rain.

What is the pH range for unpolluted rain depending on the setting?

It might range from $4.5$ to $8$ or higher.

According to Table 5.2, what are the primary sources for Nitrogen oxides ($NO_x$)?

Fossil fuel, biomass, combustion, lightning, and microbiological release.

What are the primary sources of Ammonia ($NH_3$) as listed in the transcript?

Animal excreta, fertilizers, and microbiological release.

What is the principal mechanism for the removal of $NO_x$ from the atmosphere during the daytime?

$$NO_2 + OH + M \rightarrow HNO_3 + M$$

Why is the production of nitric acid from Nitrogen oxides largely a daytime reaction?

Because it involves starting materials, such as the hydroxyl radical ($OH$), formed in part through photochemical processes.

What reaction sequence occurs after sunset to produce nitric acid ($HNO_3$) involving dinitrogen pentoxide?

$NO_3 + NO_2 \rightleftharpoons N_2O_5$ followed by $N_2O_5 + H_2O \rightarrow 2 HNO_3$

What are the products of the reaction between nitric acid and ammonia in the atmosphere?

Ammonium nitrate ($NH_4NO_3$)

Which reduced sulphur compounds are released from oceans and soils under reducing conditions?

Hydrogen sulfide ($H_2S$), Carbonyl sulfide ($COS$), methyl mercaptan, dimethyl sulfide, and dimethyl disulfide.

What is the initial product when hydrogen sulfide ($H_2S$), carbon disulfide ($CS_2$), and carbonyl sulfide ($COS$) are oxidized by hydroxyl radicals?

The thionyl radical ($SH$)

Identify the rate-determining step in the homogeneous gas-phase production of sulphuric acid.

$$SO_2 + OH + M \rightarrow HOSO_2 + M$$

In the heterogeneous production of sulphuric acid in cloud droplets, which oxidant is considered the most important?

Hydrogen peroxide ($H_2O_2$)

Provide the steady-state rate equation for the production of sulfuric acid by hydrogen peroxide oxidation of sulfur dioxide.

$$rate = \frac{d[H_2SO_4]}{dt} = \frac{k_1 k_3 [HSO_3^-][H_2O_2][H_3O^+]}{k_2 + k_3[H_3O^+]}$$

Which metals act as catalysts to increase the oxidation rate of sulphur dioxide into sulphuric acid?

Iron ($II$) and ($III$), manganese ($II$), copper ($II$), and aluminum ($III$).

What are the two compounds formed when sulphuric acid reacts with ammonia in the atmosphere?

Ammonium bisulphate ($NH_4HSO_4$) and ammonium sulphate ($(NH_4)_2SO_4$).