New Delhi: Pre-monsoon showers have been lashing Delhi for almost a month, but they have little impact on air pollution so far. In fact, until June 27, the capital witnessed a monthly average PM 2.5 level of 132 micrograms per cubic metres (g/m³) — about 2.2 times the 24-hour safe standard — which shows that Delhi's base or background emissions are quite high even when meteorological conditions are favourable.Delhi also recorded the highest pollution levels in June among major cities like Bengaluru, Chennai, Mumbai, Pune and Hyderabad.Though a direct comparison cannot be made with these cities simply because the geographical and meteorological conditions are vastly different, it underlines the fact that Delhi needs stringent enforcement of long-term action plans as well as the Supreme Court-mandated graded response plan, which came into force in January this year. Air pollution levels will fall further once monsoon arrives.The good news though is Delhi's average air quality index (AQI) for June is 164 (moderate).

The same was 189 (moderate) and 209 (poor), respectively, in the corresponding period of 2015 and 2016.Another worrying trend is that many stations are breaching the 24-hour safe standard for nitrogen dioxide (NO2)—80 g/m³. This is an indication that combustion sources are contributing to air pollution. The SC-mandated Environment Pollution Control Authority (EPCA) and CPCB had submitted a "comprehensive action plan on air pollution control in NCR" to SC in April.The draft plan prepared by CPCB, Delhi Pollution Control Committee (DPCC) and air quality experts says that annual average PM 2.5 concentrations need to be reduced by roughly 70% in Delhi to meet the annual standard of 40 g/m³.