ANALYSIS OF VEHICULAR NITROGEN OXIDES AND METEOROLOGICAL VARIABLES IN NEW DELHI

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ANALYSIS OF VEHICULAR NITROGEN OXIDES AND METEOROLOGICAL VARIABLES IN NEW DELHI

Uma Arora

Ex-Research Scientist CAS, IIT Delhi Block VI Hauz Khas New Delhi -110016

India

ABSTRACT: An analysis has been done to study the real time concentration of

vehicular nitrogen oxides (NO, NO2 & NOx ) and their correlation with meteorological

variables. The continuous hourly concentrations of NO NO2 & NOx and meteorological

variables were measured Jan.,1997- Aug.,1998.

The NO and NOx concentrations are found negatively correlated with wind

speed and temperature and positively correlated with humidity. The NO2 concentration

is positively correlated with wind speed and negatively correlated with humidity. It is found that all may be positively as well as negatively correlated with wind direction. Trend line has been calculated for each relation.

Key word index: Correlation, wind speed, Temperature, Humidity, Trend line.

1. INTRODUCTION

The present paper concentrates on vehicular pollutants NO, NO2 & NOx at a point

in the city i.e. IIT Delhi. Correlation of Nitrogen oxides with meteorological variables has been

Plotted and studied. Correlation study ( Cardenas et al.,1998 ) between CO, NOy , O3 and

non-methane hydrocarbons and their relationships with meteorology for the Norfolk coast, U.K. found that the concentrations of the chemical species were mostly a function of source characteristics with chemistry playing a minor role. Morel et. al., (1999) treated as air pollution a stochastic process and derived a probability distribution for air pollution concentration which was used to analyze the data from Santigo.

The objective of the present paper is to study the correlation of continuous hourly

measured data of NO, NO2 & NOx for 1977 and 1998 with meteorological variables

near outer ring road at IITD. Statistical analysis has been done to find the trend lines

and coefficient of correlation between NO, NO2 & NOx and meteorological variables

namely wind speed, humidity, temperature, and wind direction. The continuous

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ISSN(O): 2249-3905, ISSN(P) : 2349-6525 | Impact Factor: 6.573 | Thomson Reuters ID: L-5236-2015

between pollution data and meteorological variables have been calculated. Due to large variation in daily concentration data out of the range has been neglected. Trend lines have been obtained.

2. MONITORING SITE AND EQUIPMENT

Delhi is located at 280₃₈1_{N latitude and 77}0₁₇1_{E longitude. The air pollution}

monitoring laboratory was located inside the IIT Delhi campus. The laboratory was 10 km far from the airport, 10 km from the city centre and 28 m far from the main road – the outer ring road. The width of the road was 23.2 m. There was a boundary wall of 2m height between measuring laboratory and main road from the laboratory. As the instrument is installed near the road, all types of transport light and heavy i.e. two and three wheelers, cars, trucks, buses have been covered, though number of cars, two and three wheelers are more than heavy vehicles. On a working day number of vehicles were counted during peak hours i.e. 8-11 a.m. and 5-8 p.m. (refer Uma & Alok ,2001). HORIBA’S automatic stable air pollution monitoring system and meteorological measuring equipment were used for the measurement of data. In order to measure NO,

NO2 & NOx concentration continuously in ppm HORIBA’S APNA –350 E monitor has

been used, in which newly developed cross flow modulated (CFM) semidecompression chemiluminescene technique is used which results in remarkable zero drift performance and highest levels of sensitivity.

The manual calibration of the NO, NO2 & NOx analyzer was routinely accomplished by

the span and zero gas. The sample air flow rate was 1.5 l/m . Once in every seven days the control system switched automatically into a standard calibration. The range of

ambient NO, NO2 & NOx monitor was changed daily according to the time. The minimum

range was 0 ppm and maximum was 50 ppm. The pollutants from ambient air were sucked through glass sampling tube at the height of 4m from the ground surface. The measuring sensors for the meteorological variables, temperature and humidity, were at a height 10m and 2.8m respectively. The rotating propeller for wind speed and tail assembly for wind direction were at 10m height. The equipment allows to acquire, at its transmitter all the four meteorological variables. The converter of the equipment electrically converts the signal from each transmitter to record it continuously into an analog recorder and output it to the exterior. The output range for wind speed ,

temperature, humidity and wind direction were 0~ 30m/s, -50~50C, 0~100% and

0~540 respectively. The measuring accuracy for wind speed was better than 0.3m/s at

lower than 10m/s and better than 3% at higher than 10m/s.For temperature, humidity

and wind direction the measuring accuracies were better than 0.5C , 5% and 3

respectively. The analyzed mean hourly data of NO, NO2 & NOx and meteorological

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3. RESULTS AND DISCUSSION

The continuous hourly mean data were recorded from January 1997 to mid

August 1998 of vehicular NO, NO2 & NOx. Due to variation in data a big number of

values has been discarded. Statistical analysis was done to find the the trend lines and

coefficient of correlation between NO, NO2 & NOx and meteorological variables

namely wind speed, humidity, temperature, and wind direction. The NO and NOx concentrations are found negatively correlated with wind speed and temperature

and positively correlated with humidity. The NO2 concentration is positively correlated

with wind speed and negatively correlated with humidity. It is found that all Nitrogen oxides may be positively as well as negatively correlated with wind direction. The NO,

NO2 & NOx concentration vs. meteorological variables wind speed, humidity,

temperature and wind direction for 1977 and 1998 have been plotted in figures 1, 2

and 3 respectively. These figures show the overall trend of the NO, NO2 & NOX

concentrations with respect to four meteorological variables. In few places data was not available.

NO (in ppm) vs. METEOROLOGICAL VARIABLES

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Fig. 1

NO2 (in ppm) vs. METEOROLOGICAL VARIABLE

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Fig. 2

NOx ( in ppm) vs. METEOROLOGICAL VARIABLES

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Table 1 shows the correlation coefficients and trend lines of NO, NO2 & NOx with wind

speed, temperature, humidity and wind direction.

Vehicular

pollutant Wind Speed Humidity Temperature Wind Direction

1997

NO -0.49 0.19 -0.41 0.07

Trend line Y=-.0003x+.1044 Y=.0001x+.0441 Y=.0003x+.0979 Y=.000003x+.0572

NO2 0.40 -0.65 0.42 0.24

Trend line Y=4E-05x+.0143 Y=-8E-05x+.0306 Y=5E-05X+.013 Y=3E-05x+.0169

NOx -0.63 0.38 -0.49 -0.09

Trend line Y=-.0002x+.0858 Y=.0001x+.0361 Y=-.0002x+.0797 Y=-3e-05x+.0599

1998

NO -0.45 0.35 -0.02 -0.66

Trend line Y=-.0003x+.0709 Y=.0002x+.0259

Y=-.000003x+.0477 Y=-.0004x+.0847

NO2 0.10 -0.56 0.087 0.39

Trend line Y=2E-05x+.0192 Y=-7E-05x+0.0269 Y=-7E-05x+.0269 Y=.000004x+.0169

NOx -0.57 0.19 -0.18 -0.27

Trend line Y=-.0002x+.0679 Y=6e-05x+.0411 Y=-8e-05x+.0542 Y=-.0001x+.0579

Correlation coefficients of NO, NO2 and NOX with wind speed, Humidity, Temperature and

wind directions and trend lines. Y shows the concentration of Nitrogen oxides and variable x shows the meteorological variable. Table 1

AKNOWLEDGEMENTS

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REFERENCES

Cardenas , L.M., Austin, J.F., Burgress R.A. et. al.(1998) Correlations between CO, NOy, O3 and

non –methane hydrocarbons and their relationships with meteorology during winter 1993 on the north norfolk coast, U.K. Atmospheric Environment 32,3339-3351.