The concentration of air pollutants in ambient air is governed by the meteorological parameters such as atmospheric wind speed, wind direction, relative humidity, and temperature. This study analyses the influence of temperature and relative humidity on ambient SO2, NOx, RSPM, and SPM concentrations at North Chennai, a coastal city in India, during monsoon, post-monsoon, summer, and pre-monsoon seasons for 2010-11 using regression analysis. The results of the study show that both SO2 and NOx were negatively correlated in summer (
Industrial revolution started 200 years ago, and its consequences to human beings were recognized at the middle of 20th century. Even before epidemiological studies confirmed the existence of association between air pollution and human health, laws have been proposed to control the burning of fuels in London. Prior to 1981, there were no specific standards for Ambient Air Quality (AAQ) in India, and after enforcement of Air (Prevention and Control of Pollution) Act 1981, the first Ambient Air Quality standards were adopted in November 1982 and revised in April 1994 and again in November 2009 [
Air pollutants are being let out into the atmosphere from a variety of sources, and the concentration of pollutants in the ambient air depends not only on the quantities that are emitted but also the ability of the atmosphere, either to absorb or disperse these pollutants. Understanding the behavior of meteorological parameters in the planetary boundary layer is important because atmosphere is the medium in which air pollutants are transported away from the source, which is governed by the meteorological parameters such as atmospheric wind speed, wind direction, and temperature [
The pollution concentration in an urban area is a function of mixing depth, wind speed, and physical size of the city. The average wind speed varies more or less from place to place, from month to month and from morning to afternoon [
Dominick et al. [
Coastal atmospheric conditions widely vary from those over-inland due to the land sea interface, temperature contrast, and the consequent development of local circulations [
Chennai is a metropolitan city located on the south eastern coast of India, influenced by the coastal atmospheric conditions. The 88 number of industrial clusters in India have been identified as polluted hotspots by the Government of India and Manali of North Chennai is one among them. This study examines the influences of temperature and relative humidity on concentration variation of sulphur di oxide (SO2), nitrogen oxides (NOx), total suspended particulate matter (SPM), and respirable suspended particulate matter (RSPM) in North Chennai air basin, with respect to seasonal variation for 2010-2011.
Chennai is one of the four major metropolitan cities, located on the south east coast of India. The city is 25.6 km in length and extends inland to about 11 Km and the total area is 174 Km2. The geographical coordinates of the study area are 13°10′04′′N latitude and 80°15′43′′ E longitude and it is located at an average altitude of 6.7 metres from the sea level [
The Tamil Nadu State Pollution Control Board is operating three Continuous Ambient Air Quality Monitoring Stations (CAAQS) in the study area. One continuous monitoring station is located in Manali, and another one is at Kathivakkam and the third one is at Thiruvotriyur. (Please see Figure
Description of the study area.
The concentration levels of pollutants in the ambient air such as sulphur di oxide (SO2), nitrogen oxides (NOx), total suspended particulate matter (SPM), and respirable suspended particulate matter (RSPM) are being monitored by the State Pollution Control Board. Data related to ambient air quality were obtained from the State Pollution Control Board for this study. The meteorological parameters such as wind speed, wind direction, temperature, and relative humidity were obtained from the Indian Meteorological Department (IMD). In the present study, regression analysis procedure was attempted.
The maximum and minimum monthly average concentrations, during the period from July 2010 to June 2011, varied between 36.3
The maximum and minimum concentration level of sulphur di oxide (SO2) nitrogen oxides (NOx), total suspended particulate matter (SPM), and respirable suspended particulate matter (RSPM) recorded at the Manali, Kathivakkam and Thiruvottiyur Continuous Ambient Air Quality Monitoring Stations during pre-monsoon, monsoon, post-monsoon, and summer season from July 2010 to June 2011 are presented Table
Range of pollutant concentrations indicating season wise trend.
Pollutants | Continuous monitoring station | Pre-monsoon season | Monsoon | Post-monsoon season | Summer season | ||||
---|---|---|---|---|---|---|---|---|---|
Min |
Max |
Min |
Max |
Min |
Max |
Min |
Max |
||
SO2 | Kathivakkam | — | — | — | — | — | 36.3 | — | 27.6 |
Manali | — | 8.6 | — | — | — | — | — | ||
Thiruvottiyur | 8.1 | 17.4 | — | 15.7 | 8.1 | — | 8.5 | — | |
NOx | Kathivakkam | — | — | — | — | 11.9 | — | — | — |
Manali | — | — | 11.8 | — | — | — | — | — | |
Thiruvottiyur | 12.5 | 30.8 | 23.1 | — | 33.1 | 11.7 | 50.3 | ||
RSPM | Kathivakkam | 29 | — | 31 | — | — | — | — | 309 |
Manali | — | — | — | — | — | 225 | — | — | |
Thiruvottiyur | — | 243 | — | 292 | 40 | 35 | |||
SPM | Kathivakkam | 46 | 386 | 72 | 298 | — | 372 | — | 565 |
Manali | 46 | — | — | — | 372 | — | — | ||
Thiruvottiyur | — | — | — | — | 103 | 76 | — |
The predominant characteristic of atmosphere is its unceasing change. The temperature recorded in the study area ranged between 21°C and 33.2°C during monsoon, 21°C and 33.4°C during post-monsoon, 29°C–37.2°C during summer and 25.2°C–36.2°C during pre-monsoon seasons. The minimum temperature of 21°C was recorded during January 2011 and maximum of 37.2°C during May 2011. The monthly maximum and minimum temperature recorded from July-2010 to June 2011 are depicted graphically in Figure
Monthly temperature variation between July 2010 and June 2011.
The vertical distribution of temperature in the atmosphere varies with season and location in latitude and longitude, as well as from day to night. The temperature variations and its influence on concentrations of SO2, NOx, RSPM, and SPM in the ambient air were analyzed for monsoon, post-monsoon, summer and pre-monsoon seasons, and graphs are presented in Figure
Correlation coefficient and the regression equation between temperature and pollutants.
Season | Temperature range in °C | SO2 | NOx | RSPM | SPM | ||||
---|---|---|---|---|---|---|---|---|---|
|
Equation |
|
Equation |
|
Equation |
|
Equation | ||
Monsoon season | 21–33.2 | 0.11 | SO2 = |
0.01 | NOx = |
0.53 | RSPM = |
0.45 | SPM = |
Post-monsoon season | 21–33.4 | 0.32 | SO2 = |
0.51 | NOx = |
0.03 | RSPM = |
0.16 | SPM = |
Summer season | 29–37.2 | 0.25 | SO2 = |
0.15 | NOx = |
0.24 | RSPM = |
0.26 | SPM = |
Pre-monsoon season | 25.2–36.2 | 0.17 | SO2 = |
0 | NOx = |
0.25 | RSPM = |
0.38 | SPM = |
Correlation between temperature and SO2, NOx, RSPM, and SPM.
The results of the regression analysis revealed that SO2 and NOx have very weak but negative correlation with temperature during summer (
This study indicated significant positive correlation between temperature and SO2 and NOx during the post-monsoon, (
Gamo et al. [
The RSPM & SPM had positive correlation with temperature in summer, pre-monsoon, and monsoon season (
The probable impact due to rainfall and humidity on particulate in summer and pre-monsoon season could be generally low, when compared to monsoon and post-monsoon seasons, and the positive correlation between temperature and RSPM & SPM during summer and pre-monsoon season indicates that increase of temperature will always elevate the ambient particulate level. Grija Jayaraman [
Relative humidity ranged between 79 and 96% during monsoon, 64–98% during post-monsoon, 44 and 89% during summer, and 54 and 88% during pre-monsoon. The minimum relative humidity of 44% was recorded in summer and maximum of 98% during post-monsoon seasons. The monthly maximum and minimum relative humidity in the study area from July 2010 to June 2011 are depicted graphically in Figure
Monthly humidity variation between July 2010 and June 2011.
The season wise variations of humidity and its influence on the concentration of SO2, NOx, RSPM, and SPM were analyzed and presented in Figure
Correlation coefficient and the regression equation between humidity and pollutants.
Season | Humidity range in % | SO2 | NOx | RSPM | SPM | ||||
---|---|---|---|---|---|---|---|---|---|
|
Equation |
|
Equation |
|
Equation |
|
Equation | ||
Monsoon season | 79–96% | +13 | SO2 = |
0 | NOx = |
−51 | RSPM = |
−41 | SPM = |
Post-monsoon season | 64–98% | +35 | SO2 = |
+5 | NOx = |
−1 | RSPM = − |
−22 | SPM = |
Summer season | 44–89% | +7 | SO2 = |
0 | NOx = |
−16 | RSPM = − |
−24 | SPM = − |
Pre-monsoon season | 54–88% | 0 | SO2 = |
0 | NOx = |
−8 | RSPM = |
−3 | SPM = |
Correlation between relative humidity and SO2, NOx, RSPM, and SPM.
As seen from Table
As seen in Table
But in summer, the influence of humidity on particulate could be low because of the lower humidity range, resulting the RSPM and SPM to be weakly correlated, and coefficients of correlations are
The influences of temperature and relative humidity on the concentration of pollutants were evaluated for summer, pre-monsoon, monsoon, and post-monsoon seasons of 2010-2011 using regression analysis and the findings are stated below. The SO2 and NOx were negatively correlated with temperature during summer and monsoon, but positive during pre-monsoon and post-monsoon periods. The possible impact due to rain and humidity on the concentration of SO2, and NOx during Summer will be low when compared with other seasons. The influence of temperature on SO2 and NOx is much more effective in summer than in other seasons, due to higher temperature range. RSPM and SPM had positive correlation with temperature in summer, pre-monsoon, and monsoon season but very weak negative correlation during post-monsoon. The particulates are subjected to scrubbing process due to the rain, but during nonrainy days of monsoon period, the atmospheric temperature will increase and the concentration of particulate could be on higher side, due to the failure of natural scrubbing process. The positive correlation existing with temperature in summer clearly indicates that the increase of temperature could accelerate concentration of particulates in the ambient air. Statistically significant negative correlations were found between particulate and humidity and in all of the four seasons, and it is suggested from this study that the influence of humidity is much more effective on subsiding particulates in the coastal region.
The authors are thankful to the authorities of the Tamil Nadu Pollution Control Board, Chennai and authorities of the Indian Meteorological Department, Chennai, for their guidance to carry out this study.