Assessment of tropospheric ozone at an industrial site of Chennai megacity

Figures & data

Figure 1. (a) Map of India. (b) Map of Tamil Nadu. (c) Map showing the study area at Gummidipoondi. (d) Aerial view of monitoring location. Image sources: Maps of India (a, b); Image Source: Google Earth Pro (c, d).

Table 1. Statistical summary of the attributes monitored during the study period.

Season	Attribute	Minimum	Maximum	Mean	Std. Dev
Summer	O3 (µg/m^3)	4.32	497.23	29.66	49.31
	RH (%)	29.96	100	69.31	14.55
	T(°C)	31	41	31.77	3.046
	W.D(degrees)	0	360	158.75	62.50
	W.S(m/s)	0	7.71	3.54	1.61
	NO(µg/m^3)	0.5	58.79	12.24	4.2
	NO2(µg/m^3)	0.9	96.41	20.47	5.7
Pre Monsoon	O3(µg/m^3)	1.11	292.36	21.38	25.77
	RH(%)	32.81	100	15.19	69.33
	T(°C)	25	41	31.77	3.05
	W.D(degrees)	0	350	74.25	193.75
	W.S(m/s)	0	7.76	3.53	1.65
	NO(µg/m^3)	1.5	82.19	16.39	6.78
	NO2(µg/m^3)	1.8	114.74	24.54	12.54
Monsoon	O3(µg/m^3)	2.1	96.23	17.62	19.84
	RH(%)	32.81	100	69.34	15.19
	T(°C)	21	38	30.22	2.99
	W.D(degrees)	0	346	193.75	74.75
	W.S(m/s)	0	10.28	4.99	1.43
	NO(µg/m^3)	1.1	66.2	17.94	8.2
	NO2(µg/m^3)	1.6	100.48	28.29	10.28
Post Monsoon	O3(µg/m^3)	2.63	144.13	27.39	29.64
	RH(%)	29.72	100	71.13	14.067
	T(°C)	19	34	3.15	26.70
	W.D(degrees)	0	360	77.25	68.25
	W.S(m/s)	0	7.2	2.10	1.74
	NO(µg/m^3)	2.1	72.57	14.7	14.2
	NO2(µg/m^3)	3.0	138.01	27.5	12.7

*W.D: Wind direction; W.S: Wind speed

Table 2. Comparison of O₃ concentrations at different locations of India.

Study location	Site characteristic	Peak concentration (Season) (µg/m^3)	No. of Cases where in values exceeded NAAQS	Author and year
Gadanki	Rural	58 (Spring)	Nil	Naja and Lal 2002
Chennai	Industrial and Vehicular	135 (Summer)	Nil	Pulikesi et al. 2006
Pune	Industrial	104 (Winter)	Nil	Ali et al. 2012
Delhi	Vehicular and Industrial	152 (Post-monsoon)	Nil	Ali et al. 2012
Ooty	Clean zone	133 (Summer)	Nil	Udayasoorian et al. 2013
Mumbai	Vehicular	252 (Post-monsoon)	191 cases in 2 yr	Marathe and Murthy 2015
Gummidipoondi	Industrial and Vehicular	497.2 (Summer)	47 cases in 1 yr	Present study

Notes. Only the studies which have considered the data for the entire season are taken for comparison.

Figure 2. Time-series plot of hourly average O₃ concentrations.

Figure 3. Monthly variation of ground level O₃ concentration during the study period.

Figure 4. Monthly variation of the daily 1-hr maximum, mean daytime (11 hr from 7:00 a.m. to 6:00 p.m.), and daily (24-hr) concentrations of O_3.

Figure 5. Diurnal variation of NO, NO₂, and O_3.

Figure 6. Wind rose plots during different seasons.

Figure 7. Peculiar pattern of wind speed and wind direction.

Figure 8. Scattered polar plot showing O₃ concentrations greater than 40 μg/m³ (circles represent the observed O₃ concentration).

Table 3. Pearson’s correlation analysis of O₃ with temperature, solar irradiance, relative humidity, and NO_x during summer season (March, April, and May).

Pearson's r	T	SR	RH	NOx	O3
T	–	0.735	−0.930	0.075	0.561
SR	0.735	–	−0.789	−0.018	0.716
RH	−0.930	−0.789	–	−0.037	−0.567
NOx	0.075	−0.018	−0.037	–	0.247
O3	0.561	0.716	−0.567	0.247	–

*Correlation is significant at the 5% level.

Table 4. Pearson’s correlation analysis of O₃ with temperature, solar irradiance, relative humidity, and NO_x during pre-monsoon season (June, July, August, and September).

Pearson's r	T	SR	RH	NOx	O3
T	–	0.969	−0.976	−0.939	0.746
SR	0.969	–	−0.905	−0.833	0.751
RH	−0.976	−0.905	–	0.984	−0.656
NOx	−0.939	−0.833	0.984	–	−0.627
O3	0.746	0.751	−0.656	−0.627	–

*Correlation is significant at the 1% level.

Table 5. Pearson’s correlation analysis of O₃ with temperature, solar irradiance, relative humidity, and NO_x during monsoon season (October, November, and December).

Pearson's r	T	SR	RH	NOx	O3
T	–	0.433	0.491	0.035	−0.208
SR	0.433	–	0.002	−0.046	−0.122
RH	0.491	0.002	–	0.148	−0.265
NOx	0.035	−0.046	0.148	–	−0.533
O3	−0.208	−0.122	−0.265	−0.533	–

*Correlation is significant at the 5% level.

Table 6. Pearson’s correlation analysis of O₃ with temperature, solar irradiance, relative humidity, and NO_x during post-monsoon season (January and February).

Pearson's r	T	SR	RH	NOx	O3
T	–	0.768	−0.942	0.241	0.673
SR	0.768	–	−0.795	−0.135	0.775
RH	−0.942	−0.795	–	0.421	−0.668
NOx	0.241	−0.135	0.421	–	−0.519
O3	0.673	0.775	−0.668	−0.519	–

Notes. T = temperature; SR = solar Irradiance; RH = relative humidity; NO_x = nitrogen oxides.

Figure 9. Regression analysis. (a) O₃ with solar irradiance. (b) O₃ with temperature. (c) Negative correlation of O₃ with RH. (d) Positive correlation of O₃ with RH. (e) O₃ and NO_x during the summer months. (f) O₃ and NO_x during the monsoon months. (g) Plot showing background ozone.

Figure 10. Monthly plots of 7-day isentropic backward-trajectory analysis using HYSPLIT4 trajectory model.

Figure 10. (Continued)

Figure 11. Monthly plot (Jan–Dec) of carbon monoxide at 900 hPa obtained from MOPITT.

Figure 11. (Continued)

Figure 12. Diurnal variation of O₃ and NO_x during weekend and weekday.

Figure 13. Differences in weekend and weekday O₃ and NO_x concentrations

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