Mutual response hypothesis between surface temperature and aerosol (BC and non-BC) mass concentration observed in an urban environment

Abstract

The mutual response between near surface aerosol concentration and surface temperature works in a complicated manner. A recent study has introduced a hypothesis of mutual response between surface temperature and near surface black carbon (BC) mass concentration which states that ‘more fall in morning hour surface temperature (T) contribute to the enhancement of BC fumigation peak after the sunrise which positively impacts the extra rise in mid-day temperature over a region during the day time’. Morning hour surface temperature is proportionally linked with the strength of the night time near surface temperature inversion which contributes to the enhancement of the fumigation peak of BC aerosols after the sunrise and the enhanced fumigation peak can impact the degree of the mid-day surface temperature rise by influencing the instantaneous heating. However, it didn't mention the role of non-BC aerosols. Further, the hypothesis was drawn based on the co-located ground-based observations of surface temperature and BC concentration at a rural location of peninsular India. Though, it was mentioned that the hypothesis can be tested independently of locations, but was not thoroughly validated for an urban environment where the loading of both BC and non-BC aerosols are high. In this context, the first objective of the present work is to methodically test the BC –T hypothesis over an Indian metropolitan city, Kolkata, using the suite of measurements obtained from Kolkata Camp Observatory of NARL (KCON) along with other supporting data. In addition, the validity of the hypothesis for the non-BC fraction of PM2.5 aerosols over the same location is also tested. Besides ascertaining the above-mentioned hypothesis over an urban location, it is found that the enhancement of non-BC PM2.5 aerosols peak after the sunrise can negatively influences the mid-day temperature rise over a region during the day time.