The cities’ population all over the world is growing significantly, in order to help citizens to have the better life, authorities are trying to improving living conditions and infrastructure, however they are also facing many problems that need to be solved. Two of the most critical problems are environmental pollution and heavy traffic that are closely connected with each other.

Para One:

'The population of cities all over the world' expresses this more clearly.

Then you need to start a new sentence after significantly. At the moment you are saying that the reason they are growing significantly is to help citizens have a better life.

to improve not to improving. Many other problems (otherwise you are saying that the poor living conditions and infrastructure are not problems).

the heavy traffic

Have a look through the rest yourself. Most of your problems are caused by trying to write too complex sentences and not quite getting it right. Try simplifying your writing structure a little.

Writing topic: What are the key problems facing the world’s cities in the 21^st century and what can be done for them?

As the population of cities all over the world increases, authorities are trying to improve ("To", as in "in order to", must be followed by an infinitive: e.g., to eat, to drink, to write, to edit, etc...) people's living conditions (The word infrastructure does not make sense here), but they are facing many difficult problems. (They are facing problems that needs to be solved? Don't all problems need to be solved???) Two of the most critical problems are heavy traffic and environmental pollution, which are mutually connected because heavy traffic pollutes the environment.

Environmental pollution is (Don't use verbs/verbial clauses. They weaken your ideas and arguments.) an global issue about which many conferences annually discuss, hoping to find effective solutions.  The main reason for that (I am lost, the main reason for what?) (especially at the developing countries) is the proliferating construction of buildings and industrial zones as well as factories and plants for manufacturing many kinds of goods.

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Your turn:

- Again, use spell check; it can pick almost all of your stylistic and grammatical errors and it can save everyone a lot of time!

- Read your work over and over again, omit any unnecessary words to make your writing clearer.

Now, edit the following two paragraphs yourself. If you think you still need help, please repost!

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The appropriate allocation of urban scheme is the right answer for this problem. There should be many different divided areas for many purposes of citizens’ lives.  For example: for entertainment, there are theater and cinema combinations in the center of the city to attract the citizens to go out and have fun, for manufacturing, plants and factories should be built outside the cities and they have to be checked regularly about hygiene and drainage system problems, as well as for amusement, parks should be constructed in everywhere of the city with the open spaces, green trees, lakes and ponds for citizens to breath fresh air.

Nowadays, heavy traffic is the major problem of many countries, especially the big cities. The cause is the crowded personal transportation means including: cars, buses, trains, motorbikes…For example: the population in New York City is 18.9 million people and there are 28.2 % among them driving to work every day. Government should build public transportation widely and encourage the citizens to use it effectively as well as imposing the high tax to personal vehicles and increasing the petroleum and gas prices.