cities of similar size and similar geographical locations riga tallinn and vilnius can also vary substantively in terms of emission levels figure v the main sources of energy generation for electricity and heating purposes may explain these differences these are mainly the capitals of the eu member states while the capitals of the countries with economies in transition do face challenges in combatting the high concentration of these two pollutants figure as for the c emissions the values are also at city level and not for urban transportation only therefore further measures to limit the concentration of particulate matter would need to be applied throughout the sectors where solid and liquid fuels are combusted in particular in the energy industry and transport sectors