I don't know. Where is the pollution coming from then?
Can't you just do
Spoiler :
<PropertyManipulators>
<PropertySource>
<PropertySourceType>PROPERTYSOURCE_ATTRIBUTE_CONSTANT</PropertySourceType>
<PropertyType>PROPERTY_*POLLUTION HERE*</PropertyType>
<GameObjectType>GAMEOBJECT_CITY</GameObjectType>
<RelationType>RELATION_ASSOCIATED</RelationType>
<AttributeType>ATTRIBUTE_POPULATION</AttributeType>
<iAmountPerTurn>-2</iAmountPerTurn>
<Active>
<Greater>
<PropertyType>PROPERTY_*POLLUTION HERE*</PropertyType>
<Mult>
<AttributeType>ATTRIBUTE_POPULATION</AttributeType>
<Constant>10</Constant>
</Mult>
</Greater>
</Active>
</PropertySource>
</PropertyManipulators>
<PropertySource>
<PropertySourceType>PROPERTYSOURCE_ATTRIBUTE_CONSTANT</PropertySourceType>
<PropertyType>PROPERTY_*POLLUTION HERE*</PropertyType>
<GameObjectType>GAMEOBJECT_CITY</GameObjectType>
<RelationType>RELATION_ASSOCIATED</RelationType>
<AttributeType>ATTRIBUTE_POPULATION</AttributeType>
<iAmountPerTurn>-2</iAmountPerTurn>
<Active>
<Greater>
<PropertyType>PROPERTY_*POLLUTION HERE*</PropertyType>
<Mult>
<AttributeType>ATTRIBUTE_POPULATION</AttributeType>
<Constant>10</Constant>
</Mult>
</Greater>
</Active>
</PropertySource>
</PropertyManipulators>