greenhouse gases other than CO2
The gases N2O and CH4 are relevant greenhouse gases besides CO2. They even have a stronger warming impact per molecule. A brief summary for N2O is provided in its Wikipedia article.
Edited later on (thanks to Communisty for the comment): The global warming impact of these greenhouse gases other than CO2 is measured/presented in CO2-equivalents: i.e. the warming potential of N2O equals 298 CO2-equivalents, which means that one N2O molecule is 298 times worse than a CO2 with respect to its warming potential. Therefore, CO2 is more visible in the media.
Why focus more on CO2?
contribution to global warming
Although N2O and CH4 have a stronger greenhouse impact than CO2 per molecule, the concentrations of them are considerably lower. Therefore, in sum (heat trapping potential x number) CO2 has a stronger impact on climate change. The figure below visualizes it nicely (please find the reference below):
Figure TS.6 on page 53 of the 5th IPCC Assessment on the Physical Science Basis (www.ipcc.ch/report/ar5/wg1/).
There are also practical aspects why a focus is put on CO2: many CO2 emission sources are know and clearly to identify (combustion processes). Moreover, many of the CO2 sources are point sources. Some of them are many and small (cars) but nonetheless: we know them and know to locate them.
In contrast, N2O and CH4 emissions sources are often diffusive sources (or area sources) such as natural and agricultural soils and cattle (and other) life stock. Here you find a text and a nice figure on this topic: www.soest.hawaii.edu/mguidry/Unnamed_Site_2/Chapter%202/Chapter2C3.html
Thus, it is easier to reduce CO2 emission by specific measures: don't combust so much fuel/combustion-material.
greenhouse gases vs. air pollution
As stated above, CO2 (in sum) has a higher global warming impact (in the moment). And large parts of its emissions are easier to manage. Therefore, the focus is on CO2.
Moreover, greenhouse gas emissions have a global impact: the greenhouse gases alter the global climate. In contrast, air pollutants have a local or regional impact. Also their life time or/and residence time in the lower troposphere is shorter than the residence time of greenhouse gases in the atmosphere. Therefore, the temporal and spatial extend of greenhouse gases is larger/longer than that of air pollutants. Thus, one focuses more on the longer lasting global problem: greenhouse gases.
regional vs. global
Because greenhouse gas emissions cause global problems they are tackled on a global level -- IPCC, United Nations Climate Change Conferences, etc.
Although air pollution is also a topic dealt with on global or continental level (e.g. hemispheric transport of air pollutants (HTAP), European Monitoring and Evaluation Programme (EMEP)), it is mainly a regional or local problem.
In Europe many municipalities have recognized the problem of air pollution in cities and try to deal with it (actually, they are forced by the EU). Also in Chinese cities municipalities start working on this topic.