Influence of Biomass Burning on Temporal and Diurnal Variations of Acidic Gases, Particulate Nitrate, and Sulfate in a Tropical Urban Atmosphere

Table 2

Daytime and nighttime levels of air pollutants (unit: μg m⁻³) and meteorological parameters based on 12 hr average.

Parameters	Haze period^a					Nonhaze period^b
	Daytime^c		Nighttime^c		D/N^d	Daytime^c		Nighttime^c		D/N^d
	Mean	SD	Mean	SD		Mean	SD	Mean	SD
SO2	10.5	3.4	13.0	8.7	0.8	11.1	3.7	13.9	7.5	0.8
HONO	5.6	1.9	5.7	2.0	1.0	2.8	1.3	4.4	2.7	0.6^e
HNO3	0.6	0.5	0.2	0.1	3.0^e	0.4	0.2	0.2	0.1	2.0^e
SO4^2−	10.5	4.2	8.9	3.6	1.2	5.9	2.1	5.2	1.5	1.1
NO3^−	1.6	0.8	1.4	0.9	1.1	0.8	0.2	0.7	0.2	1.1
𝑇 (°C)	29.3	1.9	25.3	0.4	1.2^e	29.7	1.7	25.7	0.5	1.2^e
RH (%)	75.0	6.2	86.6	5.3	0.9	75.3	6.4	86.9	5.5	0.9^e
WS (m s^−1)	3.9	0.9	2.9	0.5	1.3^e	4.7	0.7	3.2	0.7	1.5^e
WD (°)	155.2	34.4	135.7	21.1	1.1	165.2	21.8	143.4	17.8	1.2^e

aHaze period from 23 August 1997 through 03 October 1997 for 11 no days; ^bnonhaze period from 24 July 1997 through 22 August for 20 no days; ^c12 hr average for both daytime and nighttime; ^dD/N = (mean concentration during daytime)/(mean concentration during nighttime); ^ethe ratio that has exhibited a significant diurnal variation at 𝑃<0.05.