A wintertime PM2.5 episode at the Fresno, CA, supersite
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Atmospheric Environment 36 (2002) 465–475
A wintertime PM2.5 episode at the Fresno, CA, supersite
John G. Watson*, Judith C. Chow
Desert Research Institute, University and Community College System of Nevada, 2215 Raggio Parkway, Reno, NV 89512, USA
Received 5 February 2001; received in revised form 24 May 2001; accepted 6 June 2001
Abstract
A winter PM2.5 episode that achieved a maximum 24-h average of 138 mg m 3 at the Fresno Supersite in California’s
San Joaquin Valley between 2 and 12 January, 2000 is examined using 5-min to 1-h continuous measurements of mass,
nitrate, black carbon, particle-bound PAH, and meteorological measurements. Every day PM2.5 sampling showed that
many episodes, including this one, are missed by commonly applied sixth-day monitoring, even though quarterly
averages and numbers of US air quality standard exceedances are adequately estimated. Simultaneous measurements at
satellite sites show that the Fresno Supersite represented PM2.5 within the city, and that half or more of the urban
concentrations were present at distant, non-urban locations unaffected by local sources. Most of the primary particles
accumulated during early morning and nighttime, decreasing when surface temperatures increased and the shallow
radiation inversion coupled to a valleywide layer. When this coupling occurred, nitrate levels increased rapidly over a
10–30 min period as black carbon and gaseous concentrations dropped. This is consistent with a conceptual model in
which secondary aerosol forms above the surface layer and is effectively decoupled from the surface for all but the late-
morning and early afternoon period. Primary pollutants, such as organic and black carbon, accumulate within the
shallow surface layer in urban areas where wood burning and vehicle exhaust emissions are high. Such a model would
explain why earlier studies find nitrate concentrations to be nearly the same among widely separated sites in urban
areas, as winds aloft of 1 to 6 m s 1 could easily disperse the elevated aerosol throughout the valley. r 2002 Elsevier
Science Ltd. All rights reserved.
Keywords: Supersite; PM2.5; Nitrate; Black carbon; Conceptual model; Fresno
1. Introduction Organic and elemental carbon are the next largest
components, constituting 20–40% of PM2.5 in urban
The highest PM2.5 and PM10 concentrations in areas, but a much smaller fraction in non-urban areas.
California’s San Joaquin Valley (SJV) occur between Ammonium sulfate and suspended dust account for the
mid-November and mid-February when several source rest of PM2.5. Suspended geological material in PM2.5 is
contributions are superimposed on each other (Chow highly variable from site to site, ranging from 1 to
et al., 1992, 1993, 1996, 1999). Secondary ammonium 9 mg m 3. Ammonium nitrate levels are similar at widely-
nitrate is the largest component, often constituting more separated monitoring sites throughout the region. The
than 50% of PM2.5 in urban areas and even more in uniformity of ammonium nitrate concentrations over
non-urban areas. Gaseous nitric acid concentrations distances of several hundred kilometers, and the
constitute only 10–20% of total nitrate during winter, separation of large ammonia emitters in non-urban
owing to an abundance of ammonia and low tempera- areas from oxide of nitrogen (NOx) emissions in distant
tures that favor the particle phase (Kumar et al., 1998). urban areas, is consistent with substantial mixing within
the 64,000 km2 air basin. Yet surface winds are sluggish
*Corresponding author. Tel.: +1-775-674-7046; fax: +1- and variable, often below detection thresholds. Daylight
775-674-7009. hours are few, sun angles are low, and surface solar
E-mail address: johnw@dri.edu (J.G. Watson). radiation is often blocked by clouds and fog. As a result,
1352-2310/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved.
PII: S 1 3 5 2 - 2 3 1 0 ( 0 1 ) 0 0 3 0 9 - 0466 J.G. Watson, J.C. Chow / Atmospheric Environment 36 (2002) 465–475 photochemical reactions that create nitric acid and road dust as well as oxides of nitrogen and sulfur dioxide ozone are slow, as indicated by maximum hourly gases from vehicle fuel combustion would build up in ground-level O3 o50 ppb at Fresno during winter, the cities during night and early morning. Non-urban compared to values >160 ppb during summer. agricultural areas distant from urban emissions would A 1995 pilot study included 3-h duration ground-level have low levels of primary particles during the morning, filter samples analyzed for primary and secondary although ammonia might accumulate near fertilized aerosol (Chow and Egami, 1997) coupled with limited fields, freestanding water, wastewater treatment facil- upper air measurements of winds and temperature ities, and livestock operations. As the surface inversion (Lehrman et al., 1998) that were used to form couples to the valleywide layer late in the morning, complementary conceptual models of these observations primary particle concentrations would decrease in the (Pun and Seigneur, 1999; Watson et al., 1998). These cities as they are diluted by mixing aloft, but they would measurements revealed that during winter nights and increase in the non-urban areas owing to downmixing mornings, a shallow (30–50 m agl) radiation surface inver- from particles mixed aloft in the cities on previous days. sion formed that only began to couple to a valleywide Secondary ammonium nitrate, and probably ammonium mixed layer (500–2000 m agl) between B0900 and sulfate, concentrations at the surface would increase B1300 PST, and re-asserted itself after sunset at after coupling between the layers during the morning, B1700 PST. During the afternoon, surface wind speeds then would slowly decrease at night owing to horizontal of 1 to 3 m s–1 were consistent with winds at higher diffusion and deposition under the shallow surface elevations within the valleywide layer. During the night radiation layer. Depending on the directions of upper and morning, however, surface winds were often air winds, which the limited measurements analyzed by o1 m s–1 while winds between the surface layer and Lehrman et al. (1998) found to be variable, emissions the top of the valleywide layer achieved speeds of 1 to throughout the valley could appreciably contribute to 6 m s–1. PM2.5 concentrations in cities more than 100 km away Between B1700 PST and B1100 PST the next morn- during a single diurnal cycle, even though surface winds ing, pollutants that mixed aloft during the B1100 to would not show transport of more than a few tens of B1700 PST period would be effectively separated from kilometers. the surface, precluding their removal by deposition to Chow et al. (1998) found some evidence of these the ground and permitting their transport over distances diurnal variations in the 3-h elemental carbon (an of 50 km (at 1 m s 1 wind speeds) to 300 km (at 6 m s–1 indicator of primary emissions) and nitrate (an indicator wind speeds) during the B16 h until surface coupling the of secondary aerosol formation) levels from urban next morning. Vertical mixing within this upper layer Fresno and Bakersfield contrasted to similar measure- would allow many pollutants to approach its top, where ments at a non-urban wildlife refuge. The averaging the sky is often cloudless and wintertime photochemistry times for the 0900 to 1200 PST and 1200 to 1500 PST might be active during the morning and afternoon samples were too long, however, to capture the rapid resulting in nitric acid formation. Between sunset and coupling that could take place according to this sunrise, and separated from fresh oxide of nitrogen conceptual model. Since the 1995 experiment, new (NO) emissions at the surface, nitrate radicals can form measurement technologies have been developed and in the upper layer that react with nitrogen dioxide (NO2) implemented at the Fresno Supersite (Watson et al., to create dinitrogen pentoxide (N2O5) (Atkinson et al., 2000a) that allow these temporal variations to be 1986; Smith et al., 1995). This N2O5 reacts with water in resolved. Valid measurements of 5 min to 1 h duration moist air or water droplets to create nitric acid at night for PM2.5 and PM10 mass, PM2.5 nitrate, black carbon, (Mentel et al., 1996; Richards, 1983). Nitric acid formed and particle-bound polycyclic aromatic hydrocarbons by these reactions, and prevented from deposition by the (PAH) were available for a January 2 through 12, 2000, surface inversion, would be available over non-urban PM2.5 episode in which PM2.5 reached a maximum of areas with high ammonia emissions to rapidly form 138 mg m 3 for the entire winter. These measurements particulate nitrate that would reach the surface after are examined here for consistency with this conceptual coupling the next morning. When valleywide layers are model with the intent to better understand and refine it. lower than mountain passes that lead to the Mojave Desert and the coast (e.g., Tehachapi Pass at the SJV’s southeast boundary, 1225 m agl), this cycle can repeat 2. Fresno supersite measurements itself for several days, thereby resulting in increasing PM2.5 concentrations, and more uniform secondary Fig. 1 shows the location of the Fresno First Street nitrate and sulfate concentrations throughout the Supersite (FSF) in the SJV and its immediate environs. region. Offices, stores, churches, and schools are located north This conceptual model implies that primary emissions and south of the Fresno Supersite on First St., a four- of particles from vehicle exhaust, home heating, and lane artery with moderate traffic levels. Land between
J.G. Watson, J.C. Chow / Atmospheric Environment 36 (2002) 465–475 467 Fig. 1. The Fresno Supersite’s location in California’s San Joaquin Valley. Clovis (CLO) is a PM2.5 compliance site. Selma (SELM) is a downwind transport site. Pixley (PIXL) is located in a non-urban wildlife refuge. Inset shows the location of the Fresno First Street (FSF) Supersite with satellite sites near a freeway on ramp (FREM) and in a nearby residential neighborhood (FRES). the many small cities and towns in the SJV is mostly how urban PM2.5 levels are incremented over regional agricultural, with nut and fruit orchards, vineyards, concentrations that derive from many sources within the cotton, corn, and alfalfa crops, and many dairies, SJV. Additional measurements are acquired at many feedlots, and chicken coops. Standing water is common other sites throughout central California by other air after rains and when crops are irrigated. quality monitoring networks (Watson et al., 1998). PM2.5 measurements at five other locations, also PM2.5 Teflon-membrane filter samples at the FSF site shown in Fig. 1, are considered here: (1) FRES are taken over 24-h periods every day using DRI represents an urban residential neighborhood located medium-volume sequential filter samplers at 20 l min 1 on a lightly-traveled side street with quarter-acre lots with Bendix 240 cyclones drawing the 113 l min 1 and houses B0.5 km east of FSF; (2) FREM is a vehicle- required for a 2.5 mm cut-point. Comparisons with a dominated site located alongside a four-lane arterial and collocated Federal Reference Method (FRM) PM2.5 a freeway on ramp in front of a row of houses B1 km sampler operated every sixth day show equivalent mass west–southwest of FSF; (3) CLO is a neighborhood concentrations. Twenty-four-hour Teflon-membrane fil- PM2.5 compliance site located in an equipment yard in ter samples at the satellite sites are taken every sixth day Fresno’s sister city of Clovis, 7 km north–northeast of using an Airmetrics Minivol sampler with PM10/PM2.5 FSF; (4) SELM is a transport site B24 km south– impactor inlets in tandem at flow rates of 5 l min 1 southeast of FSF, outside of the populated area, at a (Chow, 1995; Watson and Chow, 2002). little-used civil air field surrounded by crops and Of the many continuous measurements at the Fresno B1.6 km west of SR 99, a major north/south freeway Supersite, those used for this analysis are: (1) hourly through the SJV; and (5) PIXL is an intrabasin average PM2.5 and PM10 mass by beta attenuation transport and regionally representative site located in a monitors (BAM, van Elzakker and van der Meulen, wildlife refuge far from nearby emitters B110 km south 1989); (2) 10-min average PM2.5 nitrate by flash of FSF. These satellite sites are used to evaluate the volatilization (Stolzenburg and Hering, 2000); (3) extent to which the FSF Supersite represents outdoor 5-min average light absorption by single- and human exposure throughout the populated area and seven-wavelength aethalometers (Hansen et al., 1984);
468 J.G. Watson, J.C. Chow / Atmospheric Environment 36 (2002) 465–475
(4) 10-min average particle-bound polycyclic aromatic samples. The sixth-day samples do not allow episodes to
hydrocarbons by ultraviolet photoionization (Matter be identified and studied, however. Major episodes
et al., 1993); (5) 5-min average nitrogen oxide by showing build-up and depletion of PM2.5 are observed
chemiluminescence (Wendt et al., 1988); (6) carbon from December 13 through January 2 and again from 2
monoxide by infrared absorption (Smith et al., 1988); (7) January through 12 January. Several smaller episodes of
5-min average scalar wind speed and wind direction with shorter-duration are also evident before and after these
a low-friction cup anemometer and wind vane; (8) 5-min periods. Sixth-day sampling would not detect the 2–8, 9–
average ambient temperature with a platinum resistance 13 December, 28 December–1, 25–30 January, and 4–9
thermometer; (9) 5-min average relative humidity with a February episodes. The beginning, peak, and end of the
high-stability photovoltaic detector; and (10) 5-min 2–12 January episode would be missed by a sixth-day
average solar radiation with a capacitive chip. schedule.
Fig. 3 compares PM2.5 concentrations between the
Supersite (FSF) and the satellite sites that sample every
3. PM2.5 concentrations during winter, 1999/2000 sixth day. The FSF site appears to represent PM2.5 over
the urban area, although there are spatial deviations at
Fig. 2 shows the daily variability of PM2.5 at FSF nearby sites when PM2.5 is high. The FRES residential
from December 1999 through February 2000. PM2.5 site shows higher PM2.5 than FSF on 26 December, 1
averaged 44.4 mg m 3 for this three-month period, far in and 7 January. This is possibly caused by residential
excess of the 15 mg m 3 annual average permitted by the woodburning at homes near FRES site, which is within
US National Ambient Air Quality Standards (NAAQS, a few blocks of the site where large levoglucosan (a
U.S. EPA, 1997). Twenty-four of the 88 valid PM2.5 marker for wood smoke) concentrations were measured
measurements acquired over this period, 28% of all during the 1995 pilot study (Schauer and Cass, 2000).
measurements, exceeded the 65 mg m 3 24-h PM2.5 PM2.5 at the FREM site deviates by no more than
NAAQS, with the maximum PM2.5 of 138 mg m 3 715% from PM2.5 at the FSF site on a few days. PM2.5
measured on 9 January, 2000. The dates and shaded is nearly identical at both sites on most days, even
bars in Fig. 2 correspond to the US EPA’s sixth-day though FREM is much closer to vehicle exhaust
sampling schedule that is often followed for compliance emissions. FSF PM2.5 exceeds that at the non-urban
monitoring. The wintertime PM2.5 average for the 15 PIXL and SELM sites when PM2.5 is high, but
sixth-day samples is 43.0 mg m 3 with a maximum of concentrations are very similar among sites at the lower
127 mg m 3 on 20 December, 1999; these are similar to concentrations measured from 19 January through 24
comparable statistics for every day sampling. Twenty- February. Vigorous mixing associated with storm fronts
seven percent of the sixth-day samples exceeded during this period may have homogenized concentra-
65 mg m 3, similar to the proportion for the every day tions over large distances, although Fig. 2 indicates that
Fig. 2. Daily 24-h average PM2.5 concentrations at the Fresno Supersite (FSF) during winter 1999/2000. Light-shaded bars correspond
to the US EPA sixth-day sampling schedule and demonstrate that multi-day episodes are not represented by sporadic sampling.J.G. Watson, J.C. Chow / Atmospheric Environment 36 (2002) 465–475 469
Fig. 3. Spatial distribution of PM2.5 around the Fresno Supersite (FSF) during winter 1999/2000.
intervening samples may have shown greater variability Prior to 2 January, California was dominated by high
among the sites during episodes not characterized by the surface pressure and light winds. A surface low-pressure
sixth-day schedule. system developed in west Arizona during the early hours
PM2.5 concentrations at CLO are least related to of 1 January, tightening the pressure gradient (defining
values at FSF or at any of the other sites, even though the low pressure trough) through central California. A
the CLO site is not that distant from the FSF site. The strong upper-level low positioned off the coast of central
cause of these differences is not currently known. The California began moving eastward, weakening as it
130 mg m 3 maximum at the CLO site on 20 December traveled inland. On 2 January, the surface low moved
was only 3 mg m 3 higher than that at the FSF site, the NE into the Great Basin area over Nevada, drawing
highest of the sixth-day samples that was measured on colder air southward behind the front that brought light
the same day. The sixth-day average of 41.5 mg m 3 at precipitation to the Central Valley and most of
the CLO site is close to the averages at the FSF and California. Upper level flow (500 mb) was from the
FRES sites of 43.0 and 41.5 mg m 3, respectively. The NNW and strong (B46 m s 1).
FREM site lacked too many values for the period to Late on 2 January, the surface low quickly moved
estimate a quarterly average. Fig. 3 shows that FSF eastward and high pressure built up; the SJV was under
measurements reasonably represent concentrations over high pressure and light wind conditions until 10
a broad spatial extent within and around Fresno. This January. Trace to light precipitation occurred in north-
gives confidence that the every day samples at Fresno ern California and along coastal areas, but not in the
are sufficient to identify and analyze regionwide PM2.5 SJV. Upper level flow remained from the NW, but with
episodes. much lower intensities (from B12 m s 1 on 4 January to
B25 m s 1 on 9 and 10 January). On 11 January, a cold
frontal boundary moved southward into northern
4. 2–12 January, 2000 PM2.5 episode California, associated with a surface low forming in
SW Montana. Northern and western California received
As seen in Fig. 2, high PM2.5 concentrations were trace to light precipitation, while the SJV stayed clear.
measured throughout the month of December. Precipi- The frontal boundary moved slowly southward during
tation was negligible during this period, with the last 11 January, became stationary, and cut off on 12
storm having passed through the SJV on 13 December. 2 January. Trace amounts of precipitation were recorded
January recorded precipitation that ranged from the San in the Fresno area on 12 January, while heavier amounts
Francisco Bay area to the Sierra Nevadas and from were received to the north and west.
Chico to south of Bakersfield. Precipitation amounts Figs. 4–6 show the diurnal evolution of several
differed by location, with B0.25 mm in the Fresno area variables for 9 January (Sunday) and demonstrate many
and B0.75 mm around the PIXL site. features that occur on each day of the episode. In Fig. 4,470 J.G. Watson, J.C. Chow / Atmospheric Environment 36 (2002) 465–475 Fig. 4. Diurnal changes in PM10 (1 h), PM2.5 (1 h), nitrogen oxide (5 min), and carbon monoxide (5 min) on 9 January, 2000. Fig. 5. Diurnal changes in particle nitrate (10 min), black carbon (5 min, black carbon1 from single wavelength and black carbon7 from 880 nm channel of seven-wavelength aethalometers), particle-bound PAH (5 min), and temperature (5 min) on 9 January, 2000. the day began with PM2.5 exceeding 211 mg m 3, a nearby roadways. PM2.5 concentrations rose to decrease from 275 mg m 3 attained between 2000 and 135 mg m 3 at 1100 PST then dropped to 115 mg m 3 at 2200 PST the night before. PM2.5 levels decreased to a 1600 PST. NO and CO were at their lowest values during plateau of 112 to 117 mg m 3 between 0600 and this PM2.5 increase, indicating less accumulation of 0900 PST. The PM2.5 minimum occurred despite in- primary vehicle exhaust emissions. PM2.5 increased creases in NO and CO over the same period that are steadily after 1700 PST and in concert with increasing consistent with increased morning traffic emissions from NO and CO levels to achieve a maximum hourly level of
J.G. Watson, J.C. Chow / Atmospheric Environment 36 (2002) 465–475 471 Fig. 6. Diurnal changes in 5-min averages of wind speed, wind direction, temperature, relative humidity, and solar radiation on 9 January, 2000. 262 mg m 3 between 2300 and 2400 PST. PM10 concen- gasoline vehicle emissions (e.g. Zielinska et al., 1998). trations closely followed the PM2.5 diurnal pattern with Emissions inventories show CO and NO to be domi- the exception of the hour after 2100 PST. nated by well-maintained gasoline vehicles operating in Coarse particle mass (PM10 PM2.5) averaged the hot-stabilized mode that have low black carbon 22 mg m 3, only 11% of PM10. The 24-h average was emissions. There is not enough source information on greatly influenced by a 45 mg m 3 concentration at photoionization PAH measurements to determine how 1800 PST, and a 145 mg m 3 concentration at they are related to different particulate carbon emitters. 2100 PST. The 2100 PST hourly average alone ac- The afternoon measurements from the two aethal- counted for 28% of the 24-h average concentration. ometers are practically identical, but the morning and The simultaneous 5-min average TEOM (Tapered evening measurements for the 880 nm channel of the Element Oscillating Microbalance) measurements seven-wavelength aethalometer were 75–85% of the showed that this hourly average consisted of a 20-min single wavelength 880 nm values. pulse of coarse particles between 2045 and 2105 PST that The changes in the ratio of PAH to black carbon achieved a 5-min maximum of 316 mg m 3. throughout the day is also notable in Fig. 5. The Fig. 5 provides an explanation for the increase in photoionization method for particle-bound PAH is afternoon PM2.5. Black carbon and PAH decreased with reproducible, but at present it can only be related to PM2.5 throughout the early morning, but showed a absolute concentrations of particle-bound PAH via slight increase at 0700 and 1000 PST, similar to the CO collocated filter samples. The ratio is often near unity, and NO behavior in Fig. 4, even though PM2.5 with notable spikes that are interpreted as very fresh decreased. Nitrate decreased after 0700 PST until (o5 min aging) from nearby sources. After B1000 PST, 0920 PST, when it abruptly increased from 30 to and until B1800 PST, particle-bound PAH is substan- 52 mg m 3 when the surface temperature passed 41C. tially depleted with respect to black carbon in Fig. 5, a Black carbon decreased over a longer period surround- phenomena that occurred on all days during winter ing the nitrate increase, from 4 mg m 3 at 0840 PST to 1999/2000. This is consistent with an aged aerosol that 2.5 mg m 3 at 1025 PST. Five minute averages for PAH, has undergone photochemical transformations (e.g., CO, and NO show intermittent spikes, indicative of Chen et al., 2001). The ratio returned to unity, with pollutant wafts from nearby roadways or contributions short-duration pulses of higher ratios, into the evening. from individual high-emitters. Black carbon concentra- Nitrate remained nearly constant throughout the tions show less spikiness than PAH, CO, or NO afternoon, with a slight dip to 47 mg m 3 as temperature concentrations, indicating a more homogeneous source approached its maximum of 141C at 1500 PST. Nitrate distribution or a longer time-constant in the signal levels increased after 1500 PST as temperature de- detection. Black carbon is most abundant in diesel creased, achieving it’s highest concentration of exhaust, wood burning, and cold start or high emitting 64 mg m 3 at 1820 PST as the temperature dropped to
472 J.G. Watson, J.C. Chow / Atmospheric Environment 36 (2002) 465–475 Fig. 7. Hourly changes in nitrate and temperature for each day of the 2 January through 12 January 2000 episode. The hourly averaging smears out the rapid changes seen in the 5-min averages of Figs. 4–6, but the rapid morning increase in nitrate corresponding to a rapid increase in temperature is evident for most of the days during this episode, with the exception of 2 and 12 January when precipitation was accompanied by unstable vertical mixing conditions. 101C., then dropped to 48 mg m 3 at 1930 PST and was o1 m s 1. Fig. 6 shows that fluctuations of wind hovered at B50 mg m 3 for the rest of the day. The speeds and directions are so large over most periods that reason for the evening decrease in this case is not hourly averages reveal little about maximum speeds or understood, although it corresponds to a short-term transport directions. increase in wind speed (see Fig. 6) that may have None of the short-duration wind speeds was sufficient dispersed the cloud. The evening decrease is lower and to exceed threshold suspension velocities for wind over a longer period of time than the morning increase. erosion of fugitive dust; the abrupt increment in Fig. 6 shows how surface meteorology changed over coarse-particle concentrations between 1800 and the same period. Solar radiation increased rapidly after 2100 PST must have resulted from a local emissions sunrise at B0800 PST and returned to zero near event that introduced dust into the atmosphere rather B1800 PST after sunset. Attenuation by passing clouds than a wind erosion event. Several of these events have is evident in the rapid changes between 5-min intervals been observed in the long-term Fresno Supersite data during daylight hours. Relative humidity was inversely record for CY2000 that correspond to no recorded related to temperature, achieving a minimum of 43% at observation of nearby dust-creating activities or high 1500 PST, but maintaining levels >80% until 0900 PST wind speeds. This is consistent with previous observa- and after 2230 PST. Wind directions were highly tions (Watson et al., 2000b) that fugitive dust inventories variable during the afternoon, with predominantly miss many nearby and short-duration emissions that can northerly to northwesterly flows during morning and contribute large portions of 24-h average PM10 con- evening. Wind speeds were low, from below threshold to centrations. 1.5 m s 1. The highest wind speed of 2.9 m s 1 occurred The patterns in Figs. 4 through 6 were consistent, with at 1830 PST, although the hourly average for this period variations, for all days from 3 January through 11 of this
J.G. Watson, J.C. Chow / Atmospheric Environment 36 (2002) 465–475 473
episode. Fig. 7 illustrates changes in nitrate with
temperature, demonstrating that the 9 January behavior
is not unusual during a wintertime high-particle
concentration episode. The onset of the surface tem-
perature and nitrate increases differ from day to day,
probably owing to variable surface heating due to clouds
and surface moisture. 7 January showed a nitrate
increase from 18 to 43 mg m 3 between 1040 and
1050 PST at 5.61C. Nitrate was 45 to 57 mg m 3
throughout the early morning of 8 January, then rapidly
dropped to 34 mg m 3 at 1000 PST at a temperature of
6.31C, then rose to 57 mg m 3 at 1040 PST at a
temperature of 9.81C. On 10 January, nitrate was high
throughout the morning, achieving 52.7 mg m 3 at
0620 PST with a temperature of 21C, then dropped to
34 mg m 3 when temperature was 51C, with a rapid
increase to 57 mg m 3 at 1010 PST when temperature
was 8.11C. Nitrate on 11 January reached its minimum of
27 mg m 3 at 0810 PST and 4.21C, rising to 44.5 mg m 3 at
1100 PST and 12.21C. All days showed similar 5 min
pulses in CO, NO, and PAH, and most showed a morning
buildup and decrease in black carbon. These primary
emission indicators were always low in the afternoon,
similar to the effects shown in Figs. 4 and 5. Days prior to
7 January showed slower nitrate buildups during the
morning, sometimes later in the day than those found on Fig. 8. Pollution rose for the period of 1 January through 14
the days immediately prior to and after 9 January. January 2000. Average of 3667 5-min averages of black carbon
and particle-bound PAH and 1833 10-min average nitrate
Fig. 8 shows the directionality of pollutant origins at
concentrations for eight wind sectors. Also shown is the
FSF for the first two weeks of January 2000. Transport
fraction of wind from each sector for this period. Missing
was most frequent from the west, east, and northeast, black carbon measurements for the seven-wavelength aethalo-
and least frequent from the south and southwest. This meter were replaced with those from the collocated single
contrasts with the prevailing northwesterly flows along wavelength aethalometer. Only data records with valid mea-
the SJV axis that occur during other parts of the year. surements from all measurement systems are included in the
Black carbon and PAH levels were highest when averages.
transport was from the north and northeast, the
direction of the southbound lane on First Street. These
observables also have high values for the south and 5. Summary and conclusions
southwesterly direction, where highly traveled Shields
road is located. Nitrate concentrations did not show the Fresno Supersite measurements are consistent with
same directionality, with average concentrations of the conceptual model described above. The 24-h average
B20 mg m 3 from all directions except the east and PM2.5 measurements show increments over regional
northwest. This is further evidence that the markers for concentrations that are consistent with primary emis-
primary emissions are of urban origin whereas the sions contributed by urban traffic and residential
secondary nitrate is of regional origin. heating. Diurnally resolved measurements show that
PM2.5 was low for most of the day on 2 January as a most of the primary emissions accumulate during early
result of valleywide precipitation, but it built up rapidly morning and nighttime, decreasing when surface tem-
as primary emissions accumulated in the evening. On 12 peratures rise and vertical mixing is expected. The very
January, the high morning concentrations decreased pronounced increase in nitrate at the surface, just at the
rapidly to low levels throughout the day with dissipation time when surface temperatures rise and corresponding
of both primary and secondary components, also due to to a decrease in black carbon and PAH, shows the need
atmospheric instability associated with precipitation. for chemically-specific measurements at 5–10 min reso-
Pollution episodes do not correspond to the midnight lutions. Even an hourly average would not capture this
beginning and end points of 24-h samples. Even the change.
everyday samples shown in Fig. 2 are insufficient to fully Although Fresno Supersite measurements are consis-
understand the causes of excessive PM2.5 and PM10 tent with the conceptual model, they do not prove it. A
concentrations. more extensive upper air meteorological measurement474 J.G. Watson, J.C. Chow / Atmospheric Environment 36 (2002) 465–475
network, continuous black carbon and nitrate at other culate Air Quality Study, California Air Resources Board,
urban and rural areas, as well as above and below the Sacramento, CA, by Desert Research Institute, Reno, NV.
shallow nighttime and morning surface layer, are needed Chow, J.C., Watson, J.G., Lowenthal, D.H., Solomon, P.A.,
to confirm it and to determine the extent to which Magliano, K.L., Ziman, S.D., Richards, L.W., 1992. PM10
emissions mix throughout the SJV. Watson et al. (1998) source apportionment in California’s San Joaquin Valley.
have implemented such measurements from December Atmospheric Environment 26A, 3335–3354.
Chow, J.C., Watson, J.G., Lowenthal, D.H., Solomon, P.A.,
2000 through January 2001, and their interpretation will
Magliano, K.L., Ziman, S.D., Richards, L.W., 1993. PM10
be reported in future publications. These results from
and PM2.5 compositions in California’s San Joaquin Valley.
the Fresno Supersite demonstrate that the measurements Aerosol Science and Technology 18, 105–128.
systems are capable of capturing the chemical and Chow, J.C., Watson, J.G., Lu, Z., Lowenthal, D.H., Frazier,
temporal resolution needed to evaluate and refine the C.A., Solomon, P.A., Thuillier, R.H., Magliano, K.L.,
model. 1996. Descriptive analysis of PM2.5 and PM10 at regionally
representative locations during SJVAQS/AUSPEX. Atmo-
spheric Environment 30, 2079–2112.
Acknowledgements Chow, J.C., Watson, J.G., Lowenthal, D.H., Hackney, R.,
Magliano, K.L., Lehrman, D., Smith, T.B., 1999. Temporal
The Fresno Supersite is a cooperative effort between variations of PM2.5, PM10, and gaseous precursors during
the California Air Resources Board (ARB) and the the 1995 Integrated Monitoring Study in Central California.
Desert Research Institute (DRI). Sponsorship is pro- Air and Waste Management Association 49, PM16–PM24.
Hansen, A.D.A., Rosen, H., Novakov, T., 1984. The aethalo-
vided by the US Environmental Protection Agency
meterFan instrument for the real-time measurement of
through the Cooperative Institute for Atmospheric
optical absorption by aerosol particles. Science of the Total
Sciences and Terrestrial Applications (CIASTA) of the
Environment 36, 191–196.
National Oceanic and Atmospheric Administration and Kumar, N.K., Lurmann, F.W., Pandis, S.N., 1998. Analysis of
the California Regional PM10/PM2.5 Regional Air Atmospheric Chemistry during 1995 Integrated Monitoring
Quality Study (CRPAQS) Agency under the manage- Study. Report No. STI-997214-1791-DFR. Prepared for
ment of Ms. Karen Magliano of the ARB. The authors California Air Resources Board, Sacramento, CA, by
thank Mr. Peter Ouchida and Mr. Scott Scheller of the Sonoma Technology Inc., Santa Rosa, CA.
ARB and Dr. Suzanne Hering of Aerosol Dynamics, Lehrman, D.E., Smith, T.B., Knuth, W.R., 1998. California
Inc. for their efforts in maintaining the monitoring Regional PM10/PM2.5 Air Quality Study (CRPAQS) 1995
instruments. Dr. John Bowen, Mr. Steve Kohl, Mr. Dale Integrated Monitoring Study Data Analysis: Work element
Crow, Dr. Douglas Lowenthal, Mr. Steve Schmidt, Ms. 2.2.2 Meteorological Representativeness and Work Element
Barbara Hinsvark, and Mr. Matt Gonzi of DRI assisted 2.2.3 Fog and Low Clouds Characteristics. Prepared for
in field coordination, laboratory operations, and data California Air Resources Board, Sacramento, CA, by T&B
processing of Supersite measurements. Mr. Norman Systems, Santa Rosa, CA.
Matter, D., Burtscher, H., Kogelschatz, U., Scherrer, L.,
Mankim of DRI assisted in the assembly of this
Siegmann, H.C., 1993. Using photoemission caused by
manuscript.
excimer UV-radiation sources to characterize soot particles.
Journal of Aerosol Science 24, S365–S366.
Mentel, T.F., Bleilebens, D., Wahner, A., 1996. A study of
References nighttime nitrogen oxide oxidation in a large reaction
chamberFthe fate of NO2, N2O5, HNO3 and O3 at
Atkinson, R., Winer, A.M., Pitts Jr., J.N., 1986. Estimation of different humidities. Atmospheric Environment 30, 4007–
night-time N2O5 concentrations from ambient NO2 and 4020.
NO3 radical concentrations and the role of N2O5 in night- Pun, B.K., Seigneur, C., 1999. Understanding particulate
time chemistry. Atmospheric Environment 20, 331–339. matter formation in the California San Joaquin Valley:
Chen, J., Quan, X., Yan, Y., Yang, F., Peijnenburg, W.J.G.M., conceptual model and data needs. Atmospheric Environ-
2001. Quantitative structure-property relationship studies ment 33, 4865–4875.
on direct photolysis of selected polycyclic aromatic hydro- Richards, L.W., 1983. Comments on the oxidation of NO2 to
carbons in atmospheric aerosol. Chemosphere 42, 263–270. nitrateFDay and night. Atmospheric Environment 17,
Chow, J.C., 1995. Critical review: measurement methods to 397–402.
determine compliance with ambient air quality standards Schauer, J.J., Cass, G.R., 2000. Source apportionment of
for suspended particles. Journal of the Air and Waste wintertime gas-phase and particle-phase air pollutants using
Management Association 45, 320–382. organic compounds as tracers. Environmental Science and
Chow, J.C., Egami, R.T. 1997. San Joaquin Valley Integrated Technology 34, 1821–1832.
Monitoring Study: Documentation, Evaluation, and De- Smith, R.G., Bryan, R.J., Feldstein, M., Levadie, B., Miller,
scriptive Analysis of PM10, PM2.5, and Precursor Gas F.A., Stephens, E.R., White, N.G., 1988. Determination of
MeasurementsFTechnical Support Studies No. 4 and continuous carbon monoxide content of the atmosphere
8FFinal Report. Prepared for California Regional Parti- (nondispersive infrared method). In: Lodge, J.P. (Ed.),J.G. Watson, J.C. Chow / Atmospheric Environment 36 (2002) 465–475 475 Methods of Air Sampling and Analysis, 3rd Edition. CRC measurements from the Fresno supersite. Journal of the Air Press, Boca Raton, FL, pp. 296–302. and Waste Management Association 50, 1321–1334. Smith, N., Plane, J.M.C., Nien, C., Solomon, P.A., 1995. Watson, J.G., Chow, J.C., Pace, T.G., 2000b. Fugitive dust Nighttime radical chemistry in the San Joaquin Valley. emissions. In: Davis, W.T. (Ed.), Air Pollution Engineering Atmospheric Environment 29, 2887–2897. Manual. Van Nostrand Reinhold, New York, pp. 117–134. Stolzenburg, M.R., Hering, S.V., 2000. Method for the Watson, J.G., DuBois, D.W., DeMandel, R., Kaduwela, A.P., automated measurement of fine particle nitrate in the Magliano, K.L., McDade, C., Mueller, P.K., Ranzieri, A.J., atmosphere. Environmental Science and Technology 34, Roth, P.M., Tanrikulu, S., 1998. Field program plan for the 907–914. California Regional PM2.5/PM10 Air Quality Study US EPA 1997. National Ambient Air Quality Standards for (CRPAQS). Prepared for California Air Resources Board, Particulate Matter: Final Rule. Federal Register 62, Sacramento, CA, by Desert Research Institute, Reno, NV. 38651–38701. Wendt, J.G., Levaggi, D.A., Appel, B.R., Horstman, D.W., van Elzakker, B.G., van der Meulen, A., 1989. Performance Kothny, E.L., 1988. Continuous monitoring of atmospheric characteristics of various beta-dust monitors: intercompar- nitric oxide and nitrogen dioxide by chemiluminescence. In: ison. Journal of Aerosol Science 20, 1549–1552. Lodge, J.P. (Ed.), Methods of Air Sampling and Analysis, Watson, J.G., Chow, J.C., 2002. Ambient air sampling. In: 3rd Edition. CRC Press, Boca Raton, FL, pp. 415–421. Baron, P.A., Willeke, K. (Eds.), Aerosol Measurement: Zielinska, B., McDonald, J.D., Hayes, T., Chow, J.C., Fujita, Principles, Techniques and Applications, 2nd Edition. Van E.M., Watson, J.G., 1998. Northern Front Range Air Nostrand, Reinhold, New York, pp. 821–844. Quality Study. Volume B: Source measurements. Prepared Watson, J.G., Chow, J.C., Bowen, J.L., Lowenthal, D.H., for Colorado State University, Fort Collins, CO, Desert Hering, S.V., Ouchida, P., Oslund, W., 2000a. Air quality Research Institute, Reno, NV.
You can also read
