Air quality in Yanbu, Saudi Arabia

Figures & data

Figure 1. An overview of pollutant concentrations and environmental variables at Yanbu based on 6 yr of observations. In these graphs, the box shows the range of the middle 50% of the data, the median is at the line at the notch, the mean is the line in the box, and the whiskers are the 95% limits. These are calculated for the 24-hr average concentrations utilizing all available data. Criteria pollutants are shown in (a) NO and NO₂, (b) ozone, (c) SO₂, (d) PM_2.5 and PM₁₀, and (e) VOCs. Major environmental factors that affect air quality are shown in (f) temperature, (g) visibility, (h) cloud fraction, (i) wind direction, and (j) wind speed.

Figure 2. Factors affecting criteria pollutants at Yanbu. The difference of concentrations was calculated for conditions that lead to the highest 10% and the lowest 10% levels for the daytime averages of (a) O₃, (b) PM_2.5, and (c) SO₂. Bars to the left show negatively correlated factors and to the right show the positively related ones; 90% confidence limits of the differences are shown as the error bars. Avg = 24-hr average concentrations; Max = 1-hr maximum; Day = Daytime and Night = Nighttime, both 12-hr averages.

Figure 3. The relationship between VOCs, NO_x, and O₃ based on observed concentrations at Yanbu. (a) Daytime ozone decreases with increasing NO_x especially when NO_x exceeds about 20 ppb. (b) The relationship with VOCs is nonlinear for concentrations less than ~100 ppb; above that, ozone increases with increasing except when the VOC/NO_x ratio is low. (c) Under various VOC conditions, the maximum ozone behaves differently from the daytime average ozone. Up to NO_x levels of 20–30 ppb depending on the VOC regime, maximum hourly ozone increases with increasing NO_x, but falls dramatically once that limit is exceeded. (d) VOCs have a similar effect on maximum ozone as the daytime average ozone, except that low-VOC conditions lead to lower ozone and the highest values of hourly maximum ozone occur when both NO_x and VOCs are highest.

Figure 4. The effect of wind on the average hourly concentrations of the criteria pollutants and their precursors at Yanbu. (a) Average hourly wind speed in four categories (see text). In each wind category, we plot average hourly concentrations of fine particles (b) PM_2.5, (c) PM₁₀, (d) visibility (km), (e) SO₂, (f) temperature, (g) VOCs, (h) NO_x, and (i) ozone. The double peak of PM_2.5 concentrations is seen as caused by two different phenomena. The morning peak corresponds to the traffic mix, and the afternoon peak comes from wind blown dust, since other pollutants are low at that time. For all species, SO₂, VOCs, NO_x, and also the PM_2.5, the morning concentrations decrease with higher winds, as expected from the higher resulting dispersal rate.

Figure 5. Average hourly levels of criteria pollutants at Yanbu. The data are averaged across the 6 yr of measurements (2000–2005) showing both the average conditions and the interannual variability. (a) NO, (b) NO₂, (c) VOCs, (d) ozone, (e) PM_2.5, (f) PM₁₀, and (g) SO₂.

Figure 6. Seasonal patterns of air pollution in Yanbu. (a) NO, (b) NO₂, (c) VOCs, (d) ozone, (e) PM_2.5, and (f) SO₂.

Figure 7. The weekend effect at Yanbu. (a) to (c) show that NO, NO₂, and VOCs, respectively, are reduced during the weekend (Thursday–Friday), particularly on Fridays (−120 ± 30%, −34 ± 9%, and −12 ± 12%. Respectively, for daytime averages); however, in (d), we see that the ozone is slightly higher (+5 ± 3% for daytime averages). In (e), we see that SO₂ is also lower on Fridays (−14 ± 12% day average) and (f) the PM_2.5 particles are slightly lower.

Figure 8. Percent change of criteria pollutants during the month of Ramadan in Yanbu relative to non-Ramadan months (see text). The results indicate increased nighttime activity and reduced emissions of NO_x during the daytime.

Figure 9. Percent change of air quality during major cultural events: Eid al-Fitr, Eid al-Adha, and the Hajj.

Table 1. Standards for criteria pollutants.

	O3 (ppbv)		NO2 (ppbv)		SO2 (ppbv)				PM2.5 (μg m^−3)		PM10 (μg m^−3)
	1-hr	8-hr	1-hr	1-yr	1-hr	3-hr	24-hr	1-yr	24-hr	1-yr	24-hr	1-yr
EPA^a		75	100	53	75	500			35	12	150
WHO		50	106	21			7.6		25	10
PME^b		80	350		280		140	30
RCER^c	120	80	350	50	280		140	30	65	15	150	50

Notes: ^aEPA: PM2.5: 24-hr mean, annual 98th percentile averaged over 3 yr; PM10: 24-hr not to exceed 150 μg m⁻³ more than once per year on average over 3 yrs; SO₂: daily maximum 1-hr mean, 99th percentile averaged over 3 yr and 3-hr mean, not to be exceeded more than once per year; O₃: annual 4th highest daily maximum 8-hr mean, averaged over 3 yr; NO₂: daily maximum 1-hr mean, annual 98th percentile averaged over 3 yr. ^bPME: SO₂: 24-hr mean, not to exceeded more than once a year. ^cRCER: O₃: hourly mean, not to be exceeded more than twice a month.

Table 2. Exceedances of criteria pollutants at Yanbu.

Measurement	O3				NO2			SO2			PM2.5^b		PM10^c
	EPA	WHO	PME	RCER	EPA	WHO^a	PME/RCER	EPA	WHO	PME/RCER	WHO	RCER	EPA/RCER
Seasonal
Winter	0	123	0	1	9	5	0	25	83	2	97	30	1
Spring	6	217	1	2	6	5	1	40	103	2	72	31	7
Summer	2	119	0	2	0	0	0	37	108	1	13	4	3
Fall	1	28	0	1	11	7	0	53	136	4	61	18	5
Annual
2000	5	169	0	4	2	1	0	10	33	0
2001	1	124	0	2	6	4	0	43	98	1			0
2002	0	24	0	0	2	1	0	8	30	0	30	11	7
2003	1	96	1	0	1	0	0	18	31	0	58	19	3
2004	2	67	0	0	13	10	1	34	63	4	77	28	5
2005	0	7	0	0	1	1	0	42	175	4	79	25	1
Totals	9	487	1	6	25	17	1	155	430	9	244	83	16
Average per year	2	81	0	1	4	3	0	26	72	2	41	14	3

Notes: ^aAnnual 1. hr means for NO₂ was 22 ppb in 2004, exceeding the WHO standard in this category. ^bFor PM_2.5 and PM₁₀, data are for approximately 286 and 705 days, respectively. The rest of the time, measurements were not taken or had to be excluded because of the wind effect.

Figure 10. The EPA air quality index (AQI) applied to Yanbu for (a) ozone, (b) SO₂, and (c) PM_2.5. The index connects pollution levels directly to health impacts. At Yanbu, the air quality would be considered very good based on this index except for the high levels of fine particles that reached levels of concern during the course of the study and may be increasing. The PM_2.5 is only from those days when the winds were low enough to have an assumed negligible effect from wind blown dust as shown in Figure 4 and discussed in the text.