P. C. Manins’s research while affiliated with CSIRO Marine and Atmospheric Research and other places

Fully integrated mesoscale meterology–photochemical air pollution modelling has been underway in Australia since 1999. The focus has principally been on PC platforms using a graphical user interface, with performance and accuracy as key objectives to compare with statistical air quality objectives. Runs involving predictions for every hour for a year are commonplace. More recently, Australian integrated modelling has expanded in scale, to include synoptic scales, using clever mapping approaches and more complex photochemistries. The findings will be included in routine weather forecasting outputs as CSIRO works closely with Australian Bureau of Meteorology to build ACCESS.

Analysis of detailed tethered balloon soundings simultaneously undertaken at two sites in a valley shows that blocked (i.e. near stagnant) flow upwind of the ridges is characterized by a critical internal Froude number, Fr = uaH−1(gγa/θr)−1/2 of approximately 1.6. For Fr above this value the air in the valley is swept out by ambient wind. Otherwise blocking to near ridge height is observed. Here ua is ambient wind speed measured above ridge height H, g is acceleration due to gravity, θr a reference potential virtual temperature and γa the ambient vertical gradient of this quantity.

The performance of the Australian Air Quality Forecasting System (AAQFS) is examined by means of a case study of a 7-day photochemical smog event in the Sydney region. This was the worst smog event for the 2000/ 01 oxidant season, and, because of its prolonged nature, it provided the opportunity to demonstrate the ability of AAQFS to forecast situations involving recirculation of precursors and remnant ozone, fumigation, and complex meteorological dynamics. The forecasting system was able to successfully predict high values of ozone, although at times the peak concentrations for the inland stations were underestimated. The dynamics for the Sydney region require a sensitive balance between the synoptic and mesoscale flows. Often high concentrations of ozone were advected inland by the sea breeze. On two occasions the system forecast a synoptic flow that was too strong, which blocked the inland advancement of the sea breeze. The peak ozone forecasts were underpredicted at the inland stations on those occasions. An examination of possible factors causing forecast errors has indicated that the AAQFS is more sensitive to errors in the meteorological conditions, rather than in the emissions or chemical mechanism in the Sydney region.

A 4-day photochemical smog event in the Melbourne, Victoria, Australia, region (6 9 March 2001) is examined to assess the performance of the Australian Air Quality Forecasting System (AAQFS). Although peak ozone concentrations measured during this period did not exceed the 1-h national air quality standard of 100 ppb, elevated maximum ozone concentrations in the range of 50 80 ppb were recorded at a number of monitoring stations on all four days. These maximum values were in general very well forecast by the AAQFS. On all but the third day the system predicted the advection of ozone precursors over Port Phillip (the adjacent bay) during the morning, where, later in the day, relatively high ozone concentrations developed. The ozone was advected back inland by bay and sea breezes. On the third day, a southerly component to the background wind direction prevented the precursor drainage over the bay, and the characteristic ozone cycle was disrupted. The success of the system's ability to predict peak ozone at individual monitoring stations was largely dependent on the direction and penetration of the sea and bay breezes, which in turn were dependent on the delicate balance between these winds and the opposing synoptic flow.

The Australian Air Quality Forecasting System (AAQFS) is the culmination of a 3-yr project to develop a numerical primitive equation system for generating high-resolution (1 5 km) short-term (24 36 h) forecasts for the Australian coastal cities of Melbourne and Sydney. Forecasts are generated 2 times per day for a range of primary and secondary air pollutants, including ozone, nitrogen dioxide, carbon monoxide, sulfur dioxide, and particles that are less than 10 mum in diameter (PM10). A preliminary assessment of system performance has been undertaken using forecasts generated over a 3-month demonstration period. For the priority pollutant ozone it was found that AAQFS achieved a coefficient of determination of 0.65 and 0.57 for forecasts of peak daily 1-h concentration in Melbourne and Sydney, respectively. The probability of detection and false-alarm rate were 0.71 and 0.55, respectively, for a 60-ppb forecast threshold in Melbourne. A similar level of skill was achieved for Sydney. System performance is also promising for the primary gaseous pollutants. Further development is required before the system can be used to forecast PM10 confidently, with a systematic overprediction of 24-h PM10 concentration occurring during the winter months.

The AAQFS is routinely providing highspatial resolution air quality forecasts for guidance for the EPAs in Melbourne and Sydney. Case studies of photochemical smog events in Melbourne and Sydney have given encouraging agreement with observations. Meteorologically the two airsheds present different challenges: in Melbourne it is important to predict the onset and strength of the Port Phillip Bay breeze and the Bass Strait sea breeze; in Sydney is it important to predict the onset and strength of the Tasman sea breeze, the pollution plume trajectory for flow over complex terrain and the effects of local photochemical smog production and inter-regional transport. In the case studied for Sydney there was an additional complication of a synoptic-scale wind surge called the Southerly Buster. For both airsheds, the interaction between synoptic-scale forcing and mesoscale circulations can strongly influence the characteristics of an air pollution event and thus the meteorological model must be able to accurately simulate these interactions. In general, the LCC photochemical mechanism gave better predictions of the 1-hour ozone peak than the GRS mechanism. Improvements to the GRS mechanism and emissions inventory and online modelling of emissions and photochemistry are being developed and implemented. Work on the meteorological model to improve surface winds, soil moisture analysis and boundary-layer height also continues. We have yet to establish the limits of predictability of the system.

CSIRO's coupled meteorological and pollutant chemical dispersion model, the Air Pollution Model (TAPM), and the EPA Victoria multi-pollutant emission inventory for the Port Phillip region (including Melbourne—covering a region of approximately 24,000km2) were used to simulate 1 year of hourly averaged air pollution concentrations for smog and particles, both without and with meteorological data assimilation. Model results have been compared with data from the EPA Victoria air-monitoring network.Results show that TAPM predicts year-long extreme concentration statistics (i.e. the high end of the distribution of concentrations over 1 year) for hourly averaged smog (NO2 and O3) to within 9%, and for 24-hourly averaged particles (PM10 and PM2.5) to within 13%, averaged across all monitoring sites, even when no local meteorological data are assimilated into the model. Results for paired-in-time measures such as correlation coefficient, factor-of-two and gross error, also show that TAPM is performing well, with average values (averaged over all monitoring sites) of 0.51, 0.76 and 0.38 for these measures, respectively. Results for the simulation with meteorological data assimilation were very close to those from the simulation without meteorological data assimilation. The good results obtained with the model also indicate that the emission inventory is of a high quality.

A versatile tethered balloon sounding system capable of measuring horizontal-vector wind, temperature, humidity and pressure altitude is described. It has a novel combination of features which include low weight, low power consumption, completely self-contained operation and good data accuracy at reasonable cost.