Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_2780146_6 (standard VARCHAR, pm__g_kwh_ VARCHAR)

### Question ###
How many different standards have a PM of 0.02 g/kWh?

### Accurate SQL ###

SELECT COUNT(standard) FROM table_2780146_6 WHERE pm__g_kwh_ = "0.02"