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Poor air quality is recognised as the most important environmental health issue of our time. Meteorological variables like temperature and wind speed can strongly influence air quality and these variables often show clear annual cycles. It is therefore common to analyse atmospheric pollutants within a seasonal framework. However, the commonly used seasons in Australia do not align well with all of the most important annual weather patterns that influence air quality in the Sydney Basin. We used Indigenous perspectives on ‘seasons’ as identified by the co-authors and combined these with statistical analysis of the local climatology. This enabled us to create a set of locally informed ‘quasi-seasons’ that we named IKALC-seasons (Indigenous Knowledge Applied to Local Climatology). Engaging with the IKALC-seasons improved our understanding of temporal variability of air pollution in western Sydney, mainly due to a better identification of the time of year when cold, still weather conditions result in higher levels of fine particulate pollution, carbon monoxide and nitrogen oxides. Although the IKALC seasons identified in this study are intrinsically local in nature, the methodology developed has broadscale application. This approach can be used to identify the times of year when micrometeorological conditions are most likely to drive poor air quality thereby helping to inform effective decision-making about emission controls.

The remoteness and extreme conditions of the Southern Ocean and Antarctic region have meant that observations in this region are rare, and typically restricted to summertime during research or resupply voyages. Observations of aerosols outside of the summer season are typically limited to long-term stations, such as Kennaook / Cape Grim (KCG; 40.7∘ S, 144.7∘ E), which is situated in the northern latitudes of the Southern Ocean, and Antarctic research stations, such as the Japanese operated Syowa (SYO; 69.0∘ S, 39.6∘ E). Measurements in the midlatitudes of the Southern Ocean are important, particularly in light of recent observations that highlighted the latitudinal gradient that exists across the region in summertime. Here we present 2 years (March 2016–March 2018) of observations from Macquarie Island (MQI; 54.5∘ S, 159.0∘ E) of aerosol (condensation nuclei larger than 10 nm, CN10) and cloud condensation nuclei (CCN at various supersaturations) concentrations. This important multi-year data set is characterised, and its features are compared with the long-term data sets from KCG and SYO together with those from recent, regionally relevant voyages. CN10 concentrations were the highest at KCG by a factor of ∼50 % across all non-winter seasons compared to the other two stations, which were similar (summer medians of 530, 426 and 468 cm−3 at KCG, MQI and SYO, respectively). In wintertime, seasonal minima at KCG and MQI were similar (142 and 152 cm−3, respectively), with SYO being distinctly lower (87 cm−3), likely the result of the reduction in sea spray aerosol generation due to the sea ice ocean cover around the site. CN10 seasonal maxima were observed at the stations at different times of year, with KCG and MQI exhibiting January maxima and SYO having a distinct February high. Comparison of CCN0.5 data between KCG and MQI showed similar overall trends with summertime maxima and wintertime minima; however, KCG exhibited slightly (∼10 %) higher concentrations in summer (medians of 158 and 145 cm−3, respectively), whereas KCG showed ∼40 % lower concentrations than MQI in winter (medians of 57 and 92 cm−3, respectively). Spatial and temporal trends in the data were analysed further by contrasting data to coincident observations that occurred aboard several voyages of the RSV Aurora Australis and the RV Investigator. Results from this study are important for validating and improving our models and highlight the heterogeneity of this pristine region and the need for further long-term observations that capture the seasonal cycles.

Little overlap exists in the required capabilities of 222Rn (radon) monitors for public health and atmospheric research. The former requires robust, compact, easily transportable instruments to characterise daily to yearly variability >100 Bq m−3, whereas the latter requires static instruments capable of characterising sub-hourly variability between 0.1 and 100 Bq m−3. Consequently, detector development has evolved independently for the two research communities, and while many radon measurements are being made world-wide, the full potential of this measurement network can't be realised because not all results are comparable. Development of a monitor that satisfies the primary needs of both measurement communities, including a calibration traceable to the International System of Units (SI), would constitute an important step toward (i) increasing the availability of radon measurements to both research communities, and (ii) providing a means to harmonize and compare radon measurements across the existing eclectic global network of radon detectors. To this end, we describe a prototype detector built by the Australian Nuclear Science and Technology Organisation (ANSTO), in collaboration with the EMPIR 19ENV01 traceRadon Project and Physikalisch-Technische Bundesanstalt (PTB). This two-filter dual-flow-loop radon monitor can be transported in a standard vehicle, fits in a 19′′ instrument rack, has a 30 min temporal resolution, and a detection limit of ∼0.14 Bq m−3. It is capable of continuous, long-term, low-maintenance, low-power, indoor or outdoor monitoring with a high sensitivity and an uncertainty of ∼15 % at 1 Bq m−3. Furthermore, we demonstrate the successful transfer of an SI traceable calibration from this portable monitor to a 1500 L two-filter radon monitor under field conditions.

Four years of observations of radon, meteorology and atmospheric pollution was used to demonstrate the efficacy of combined diurnal and synoptic timescale radon-based stability classification schemes in relating atmospheric mixing state to urban air quality in Zgierz, Central Poland. Nocturnal radon measurements were used to identify and remove periods of non-stationary synoptic behaviour (13–18% of each season) and classify the remaining data into five mixing states, including persistent temperature inversion (PTI) conditions, and non-PTI conditions with nocturnal conditions ranging from well mixed to stable. Mixing state classifications were performed completely independently of site meteorological measurements. World Health Organization guideline values for daily PM2.5/PM10 were exceeded only under strong PTI conditions (3–15% of non-summer months) or often under non-PTI stable nocturnal conditions (14–20% of all months), when minimum nocturnal mean wind speeds were also recorded. In non-summer months, diurnal amplitudes of NO (CO) increased by the factors of 2–12 (3–7) from well-mixed nocturnal conditions to PTI conditions, with peak concentrations occurring in the morning/evening commuting periods. Analysis of observations within radon-derived atmospheric mixing ‘class types’ was carried out to substantially clarify relationships between meteorological and air quality parameters (e.g. wind speed vs. PM2.5 concentration, and atmospheric mixing depth vs. PM10 concentration).

The use of the noble gas radon ( 222Rn ) as a tracer for different research studies, for example observation-based estimation of greenhouse gas (GHG) fluxes, has led to the need of high-quality 222Rn activity concentration observations with high spatial and temporal resolution. So far a robust metrology chain for these measurements is not yet available. A portable direct atmospheric radon monitor (ARMON), based on electrostatic collection of 218Po , is now running at Spanish stations. This monitor has not yet been compared with other 222Rn and 222Rn progeny monitors commonly used at atmospheric stations. A 3-month intercomparison campaign of atmospheric 222Rn and 222Rn progeny monitors based on different measurement techniques was realized during the fall and winter of 2016–2017 to evaluate (i) calibration and correction factors between monitors necessary to harmonize the atmospheric radon observations and (ii) the dependence of each monitor's response in relation to the sampling height and meteorological and atmospheric aerosol conditions. Results of this study have shown the following. (i) All monitors were able to reproduce the atmospheric radon variability on a daily basis. (ii) Linear regression fits between the monitors exhibited slopes, representing the correction factors, between 0.62 and 1.17 and offsets ranging between −0.85 and −0.23 Bq m −3 when sampling 2 m above ground level (a.g.l.). Corresponding results at 100 m a.g.l. exhibited slopes of 0.94 and 1.03 with offsets of −0.13 and 0.01 Bq m −3 , respectively. (iii) No influence of atmospheric temperature and relative humidity on monitor responses was observed for unsaturated conditions at 100 m a.g.l., whereas slight influences (order of 10−2 ) of ambient temperature were observed at 2 m a.g.l. (iv) Changes in the ratio between 222Rn progeny and 222Rn monitor responses were observed under very low atmospheric aerosol concentrations. Results also show that the new ARMON could be useful at atmospheric radon monitoring stations with space restrictions or as a mobile reference instrument to calibrate in situ 222Rn progeny monitors and fixed radon monitors. In the near future a long-term comparison study between ARMON, HRM, and ANSTO monitors would be useful to better evaluate (i) the uncertainties of radon measurements in the range of a few hundred millibecquerels per cubic meter to a few becquerels per cubic meter and (ii) the response time correction of the ANSTO monitor for representing fast changes in the ambient radon concentrations.

Coral reefs have been found to produce the sulfur compound dimethyl sulfide (DMS), a climatically relevant aerosol precursor predominantly associated with phytoplankton. Until recently, the role of coral-reef-derived DMS within the climate system had not been quantified. A study preceding the present work found that DMS produced by corals had negligible long-term climatic forcing at the global–regional scale. However, at sub-daily timescales more typically associated with aerosol and cloud formation, the influence of coral-reef-derived DMS on local aerosol radiative effects remains unquantified. The Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) has been used in this work to study the role of coral-reef-derived DMS at sub-daily timescales for the first time. WRF-Chem was run to coincide with an October 2016 field campaign over the Great Barrier Reef, Queensland, Australia, against which the model was evaluated. After updating and scaling the DMS surface water climatology, the model reproduced DMS and sulfur concentrations well. The inclusion of coral-reef-derived DMS resulted in no significant change in sulfate aerosol mass or total aerosol number. Subsequently, no direct or indirect aerosol effects were detected. The results suggest that the co-location of the Great Barrier Reef with significant anthropogenic aerosol sources along the Queensland coast prevents coral-reef-derived aerosol from having a modulating influence on local aerosol burdens in the current climate.

This paper summarizes and analyses available data on the surface energy balance of Arctic tundra and boreal forest. The complex interactions between ecosystems and their surface energy balance are also examined, including climatically induced shifts in ecosystem type that might amplify or reduce the effects of potential climatic change. High latitudes are characterized by large annual changes in solar input. Albedo decreases strongly from winter, when the surface is snow-covered, to summer, especially in nonforested regions such as Arctic tundra and boreal wetlands. Evapotranspiration (QE) of high-latitude ecosystems is less than from a freely evaporating surface and decreases late in the season, when soil moisture declines, indicating stomatal control over QE, particularly in evergreen forests. Evergreen conifer forests have a canopy conductance half that of deciduous forests and consequently lower QE and higher sensible heat flux (QH). There is a broad overlap in energy partitioning between Arctic and boreal ecosystems, although Arctic ecosystems and light taiga generally have higher ground heat flux because there is less leaf and stem area to shade the ground surface, and the thermal gradient from the surface to permafrost is steeper. Permafrost creates a strong heat sink in summer that reduces surface temperature and therefore heat flux to the atmosphere. Loss of permafrost would therefore amplify climatic warming. If warming caused an increase in productivity and leaf area, or fire caused a shift from evergreen to deciduous forest, this would increase QE and reduce QH. Potential future shifts in vegetation would have varying climate feedbacks, with largest effects caused by shifts from boreal conifer to shrubland or deciduous forest (or vice versa) and from Arctic coastal to wet tundra. An increase of logging activity in the boreal forests appears to reduce QE by roughly 50% with little change in QH, while the ground heat flux is strongly enhanced.

Black carbon (BC) aerosols significantly contribute to radiative budgets globally, however their actual contributions remain poorly constrained in many under-sampled ocean regions. The tropical waters north of Australia are a part of the Indo-Pacific warm pool, regarded as a heat engine of global climate, and are in proximity to large terrestrial sources of BC aerosols such as fossil fuel emissions, and biomass burning emissions from northern Australia. Despite this, measurements of marine aerosols, especially BC remain elusive, leading to large uncertainties and discrepancies in current chemistry-climate models for this region. Here, we report the first comprehensive measurements of aerosol properties collected over the tropical warm pool in Australian waters during a voyage in late 2019. The non-marine related aerosol emissions observed in the Arafura Sea region were more intense than in the Timor Sea marine region, as the Arafura Sea was subject to greater continental outflows. The median equivalent BC (eBC) concentration in the Arafura Sea (0.66 μg m

International audience; Radon gas is the largest source of public exposure to naturally occurring radioactivity. However, radon is also a useful tracer for understanding atmospheric processes, assessing the accuracy of chemical transport models, and enabling integrated emissions estimates of greenhouse gases. A sound metrological system for low level atmospheric radon observations is therefore needed for the benefit of the atmospheric, climate and radiation protection research communities. To this end, here we present a new calibration method for activity concentrations below 20 Bq m−3 and a prototype of the first portable radon monitor capable of achieving uncertainties of 5% (at k = 2) at these concentrations. Compliance checking of policy-driven regulations regarding greenhouse gas (GHG) emissions is an essential component of climate change mitigation efforts. Independent, reliable 'top down' methods that can be applied consistently for estimating local- to regional-scale GHG emissions (such as the radon tracer method (RTM)) are an essential part of this process. The RTM relies upon observed radon and GHG concentrations and measured or modeled radon fluxes. Reliable radon flux maps could also significantly aid EU member states comply with European COUNCIL DIRECTIVE 2013/59/EURATOM. This article also introduces the traceRadon project, key aims of which include outlining a standardized approach for application of the RTM, creating infrastructure with a traceability chain for radon concentration and radon flux measurements, and developing tools for the validation of radon flux models. Since radon progeny dominate the terrestrial gamma dose rate, the planned traceRadon activities are also expected to improve the sensitivity of radiation protection early warning networks because of the correlation known to exist between radon flux and ambient equivalent dose rates.

Coral reefs have been found to produce the sulfur compound dimethyl sulfide (DMS), a climatically relevant aerosol precursor predominantly associated with phytoplankton. Until recently, the role of coral reef-derived DMS within the climate system had not been quantified. A study preceding the present work found that DMS produced by corals had negligible long-term climatic forcing at the global-regional scale. However, at sub-daily time scales more typically associated with aerosol and cloud formation, the influence of coral reef-derived DMS on local aerosol radiative effects remains unquantified. The Weather Research and Forecasting – chemistry model (WRF-Chem) has been used in this work to study the role of coral reef-derived DMS at sub-daily time scales for the first time. WRF-Chem was run to coincide with an October 2016 field campaign over the Great Barrier Reef, Queensland, Australia, against which the model was evaluated. After updating the DMS surface water climatology, the model reproduced DMS and sulfur concentrations well. The inclusion of coral reef-derived DMS resulted in no significant change in sulfate aerosol mass or total aerosol number. Subsequently, no direct or indirect aerosol effects were detected. The results suggest that the co-location of the Great Barrier Reef with significant anthropogenic aerosol sources along the Queensland coast prevents coral reef derived-aerosol from having a modulating influence on local aerosol burdens in the current climate.

Sea salt is one of the major aerosols in the atmosphere in both the fine and coarse size ranges. Newly formed sea salt particles have a similar composition to seawater; including elements such as Na, Cl, Mg, S, Ca, Br and K. However, once in the atmosphere sea salt particles can undergo chemical reactions with other airborne pollutants, resulting in a loss of chlorine (whereas Na is conservative). The modified aerosol is commonly referred to as aged sea spray or aged sea salt. Fine aerosols from two sites in the Sydney Basin were analysed for source fingerprints with components that may have originated from the ocean (i.e. fresh and aged sea spray). At Lucas Heights, 18.4 km from the nearest coast, the average source fingerprint concentrations of fresh and aged sea spray were 0.47 ± 0.02 and 1.08 ± 0.03 μg/m3, respectively. At Richmond, 58 km from the coast, the average fingerprint concentrations of fresh and aged sea spray were 0.26 ± 0.01 and 0.87 ± 0.02 μg/m3, respectively. At Lucas heights, fresh and aged sea spray contributed to 11% and 21% of PM2.5, respectively. At Richmond fresh and aged sea spray contributed to 4.8 ± 0.35 and 16 ± 0.5% of the PM2.5, respectively. The Cl/Na ratios of aged sea spray at Lucas Heights and Richmond were 0.72 and 0.87, respectively, in comparison to 1.54 for fresh sea salt. At Richmond the corresponding Ca/Na and K/Na ratios were both 0.037 (close to that of seawater), and at Lucas Heights, the corresponding ratios were 0.038 and 0.026, respectively. Back trajectory and Radon-222 analysis demonstrated that the largest concentrations of aged sea spray occur when the air masses had travelled over regions of anthropogenic sources. This confirms an interaction between anthropogenic precursors and sea spray that liberates chlorine enabling it to contribute to other chemical reactions in the atmosphere, e.g. resulting in an increase in the formation of ozone.

An overlapping need exists between the climate science, air quality and radiological protection communities for a robust, portable and direct monitor of atmospheric 222Rn concentrations typical of the ambient outdoor atmosphere. To reliably characterise afternoon radon concentrations, or resolve daytime vertical radon gradients in the atmospheric boundary layer (requirements for radon measurements to be used to evaluate the performance of chemical transport models), detection limits of ≤0.2 Bq m-3 at an hourly temporal resolution are required. Commercial portable radon detectors are mainly designed for indoor use, and the best of these has a detection limit of ≥2 Bq m-3 for hourly sampling, with an approximate uncertainty of 60% at typical outdoor daytime radon concentrations. Here we introduce a portable (200 L) version of the two-filter dual-flow-loop radon detector, designed and built by ANSTO in collaboration with the EMPIR 19ENV01 traceRadon project. While not as compact as commercial monitors (standing 1.6 m tall, and 0.48 m wide), its longest component is 1.2 m, enabling transportation in a standard utility vehicle or 4x4 (and can fit inside a 19” instrument rack). Constructed of marine grade stainless steel, it is weather resistant, robust, and suitable for long-term, continuous, autonomous deployment; in fact it is fully remotely controllable if a networked computer is available. The estimated lower limit of detection is 0.17 Bq m-3 for hourly observations, and the counting uncertainty at typical ambient outdoor radon concentrations is around 7%. Additional uncertainty associated with current calibration techniques, which inject calibration gas on top of ambient sampled air, varies from 2-6%. Some objectives of the traceRadon project include establishing direct calibration traceability to the SI and developing an improved closed-loop calibration technique, using a new, low activity Radium-226 source. If successful, the absolute accuracy of the 200 L radon detector at typical ambient outdoor concentrations could be kept well below 15% for hourly observations. This project has received funding from the EMPIR programme co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme. 19ENV01 traceRadon denotes the EMPIR project reference.

Data repository for paper: "Simulation of radon-222 with the GEOS-Chem global model: Emissions, seasonality, and convective transport" by Bo Zhang, Hongyu Liu, James H. Crawford, Gao Chen, T. Duncan Fairlie, Scott Chambers, Chang-Hee Kang, Alastair G. Williams, Kai Zhang, David B. Considine, Daniel J. Jacob, Melissa P. Sulprizio, and Robert M. Yantosca, submitted to Atmos. Chem. Phys., July 2020 Created by Bo Zhang (bzhang@nianet.org), July 2020 -> Data -> Rn_surface Contains site measurement files -> Please refer to Zhang et al. (2011) for most of the surface site measurements. -> MLO_radon.xlsx Long-term Rn-222 measurements at Mauna Loa. -> Gosan_2001-2010.xlsx Long-term Rn-222 measurements at Gosan. -> Rn_profile Contains no data here. Please refer to Liu et al. (1984), Kritz et al. (1998), Zaucker et al. (1996), and Williams et al. (2011) for the four Rn-222 profile datasets. -> Model_modified -> Code_1101f_Rn_paper The folder contains a complete code directory of GEOS-Chem v11-01f. -> hcox_gc_RnPbBe_mod.F90.ZKCHA120NASWred This file replaces HEMCO/Extensions/hcox_gc_RnPbBe_mod.F90 under GEOS-Chem version 11.01f code directory to read the updated emission files (Rn_emis_ZKCHA120_NASWred). Search 'bz' in the file for modifications. -> Rn_emis_ZKCHA120_NASWred: updated global Rn-222 emission fluxes. -> ZKC_EMIS_ARR_ATOM_2X25_MONTHLY.sav IDL save-file with saved monthly mean Rn-222 emission fluxes. (gridded 2x2.5 array ZKC_EMIS_ARR_ATOM_2X25_MONTHLY) Unit is atom Rn-222 per cm2 per second. -> Rn_emis_ZKCHA120_NASWred_2x25_std01-12 Text files need to be put under GEOS-Chem run directory. Each monthly file contains a single column array. The data are placed in a longitude and latitude sequence starting from (180W, 89.5S) to (178W, 89.5S) .... and until (177.5E, 89.5N). The entire folder needs to be placed under GEOS-Chem run directory. -> For the other three emission scenarios used in the paper please refer to Jacob et al. (1997), Schery and Wasiolek (1998), and Zhang et al. (2011). -> Model_output -> tracerinfo.dat, diaginfo.dat: GEOS-Chem dat files needed for IDL-GAMAP -> rpbbe2_1101f_merra_2013_JA97.bpch: model output with emission JA97. -> rpbbe2_1101f_merra_2013_SW98.bpch: model output with emission SW98. -> rpbbe2_1101f_merra_2013_ZK11.bpch: model output with emission ZK11. -> rpbbe2_1101f_merra_2013_ZKCHA120NASWred.bpch: model output with the updated emission in this work. Reference: Jacob, D. J., Prather, M. J., Rasch, P. J., Shia, R. L., Balkanski, Y. J., Beagley, S. R., ... & Chipperfield, M. P. (1997). Evaluation and intercomparison of global atmospheric transport models using 222Rn and other short‐lived tracers. Journal of Geophysical Research: Atmospheres, 102(D5), 5953-5970. Kritz, M. A., Rosner, S. W. and Stockwell, D. Z.: Validation of an off-line three-dimensional chemical transport model using observed radon profiles: 1. Observations, J. Geophys. Res, 103, 8425–8432, 1998. Liu, S. C., Mcafee, J. R. and Cicerone, R. J.: Radon 222 and Tropospheric Vertical Transport, J. Geophys. Res., 89(20), 7291–7297, doi:10.1029/JD089iD05p07291, 1984. Schery, S. D. and Wasiolek, M. A.: Modeling radon flux from the Earth’s surface, in: Radon and Thorn in the Human Environment, in: Proceedings of the 7th Tohwa University International Symposium, edited by: Katase, A. and Shimo, M., World Scientific Publishing Co. Pre. Ltd., Singapore, 73–78, 1998. Williams, A. G., Zahorowski, W., Chambers, S., Griffiths, A., Hacker, J. M., Element, A. and Werczynski, S.: The vertical distribution of radon in clear and cloudy daytime terrestrial boundary layers, J. Atmos. Sci., 68(1), 155–174, doi:10.1175/2010JAS3576.1, 2011. Zaucker, F., PH, and D., U, W., Berkowitz, C., nd Kromer, B. and Broecker, W. S.: Atmospheric 222Rn measurements during the 1993 NARE Intensive., J. Geophys. Res., 101, 29149–29164, 1996. Zhang, K., Feichter, J., Kazil, J., Wan, H., Zhuo, W., Griffiths, A., ... & Yver, C. (2011). Radon activity in the lower troposphere and its impact on ionization rate: a global estimate using different radon emissions. Atmospheric Chemistry and Physics, 11(15), 7817-7838. &nbsp

Volatile organic compounds (VOCs) play a key role in the formation of ozone and secondary organic aerosol, the two most important air pollutants in Sydney, Australia. Despite their importance, there are few available VOC measurements in the area. In this paper, we discuss continuous GC-MS measurements of 10 selected VOCs between February (summer in the southern hemisphere) and June (winter in the southern hemisphere) of 2019 in a semi-urban area between natural eucalypt forest and the Sydney metropolitan fringe. Combined, isoprene, methacrolein, methyl-vinyl-ketone, &alpha, pinene, p-cymene, eucalyptol, benzene, toluene xylene and tri-methylbenzene provide a reasonable representation of variability in the total biogenic VOC (BVOC) and anthropogenic VOC (AVOC) loading in the area. Seasonal changes in environmental conditions were reflected in observed BVOC concentrations, with a summer peak of 8 ppb, dropping to approximately 0.1 ppb in winter. Isoprene, and its immediate oxidation products methacrolein (MACR) and methyl-vinyl-ketone (MVK), dominated BVOC concentrations during summer and early autumn, while monoterpenes comprised the larger fraction during winter. Temperature and solar radiation drive most of the seasonal variation observed in BVOCs. Observed levels of isoprene, MACR and MVK in the atmosphere are closely related with variations in temperature and photosynthetically active radiation (PAR), but chemistry and meteorology may play a more important role for the monoterpenes. Using a nonlinear model, temperature explains 51% and PAR 38% of the isoprene, MACR and MVK variation. Eucalyptol dominated the observed monoterpene fraction (contributing ~75%), with p-cymene (20%) and &alpha, pinene (5%) also present. AVOCs maintain an average concentration of ~0.4 ppb, with a slight decrease during autumn&ndash, winter. The low AVOC concentrations observed indicate a relatively small anthropogenic influence, generally occurring when (rare) northerly winds transport Sydney emissions to the measurement site. The site is influenced by domestic, commercial and vehicle AVOC emissions. Our observed AVOC concentrations can be explained by the seasonal changes in meteorology and the emissions in the area as listed in the NSW emissions inventory and thereby act as an independent validation of this inventory. We conclude that the variations in atmospheric composition observed during the seasons are an important variable to consider when formulating air pollution control policies over Sydney given the influence of biogenic sources during summer, autumn and winter.

Aerosol measurements over the Southern Ocean have been identified as critical to an improved understanding of aerosol–radiation and aerosol–cloud interactions, as there currently exists significant discrepancies between model results and measurements in this region. The atmosphere above the Southern Ocean provides crucial insight into an aerosol regime relatively free from anthropogenic influence, yet its remoteness ensures atmospheric measurements are relatively rare. Here we present observations from the Polar Cell Aerosol Nucleation (PCAN) campaign, hosted aboard the RV Investigator during a summer (January–March) 2017 voyage from Hobart, Australia, to the East Antarctic seasonal sea ice zone. A median particle number concentration (condensation nuclei > 3 nm; CN3) of 354 (95 % CI 345–363) cm−3 was observed from the voyage. Median cloud condensation nuclei (CCN) concentrations were 167 (95 % CI 158–176) cm−3. Measured particle size distributions suggested that aerosol populations had undergone significant cloud processing. To understand the variability in aerosol observations, measurements were classified by meteorological variables. Wind direction and absolute humidity were used to identify different air masses, and aerosol measurements were compared based on these identifications. CN3 concentrations measured during SE wind directions (median 594 cm−3) were higher than those measured during wind directions from the NW (median 265 cm−3). Increased frequency of measurements from these wind directions suggests the influence of large-scale atmospheric transport mechanisms on the local aerosol population in the boundary layer of the East Antarctic seasonal ice zone. Modelled back trajectories imply different air mass histories for each measurement group, supporting this suggestion. CN3 and CCN concentrations were higher during periods where the absolute humidity was less than 4.3 gH2O/m3, indicative of free tropospheric or Antarctic continental air masses, compared to other periods of the voyage. Increased aerosol concentration in air masses originating close to the Antarctic coastline have been observed in numerous other studies. However, the smaller changes observed in the present analyses suggest seasonal differences in atmospheric circulation, including lesser impact of synoptic low-pressure systems in summer. Further measurements in the region are required before a more comprehensive picture of atmospheric circulation in this region can be captured and its influence on local aerosol populations understood.

The generally-accepted paradigm of wetland response to climate change is that water table drawdown and higher temperatures will cause wetlands to switch from a sink to a source of atmospheric carbon. However, it is hard to find a multi-year, ecosystem scale dataset representative of an undisturbed wetland that clearly demonstrates this paradigm on an annual total basis. Here we provide strong empirical confirmation of the above scenario based on six years of continuous eddy-covariance CO2 and CH4 flux measurements in Biebrza Valley, north-eastern Poland. In wet years the mire was a significant sink of atmospheric carbon (down to −270 ± 70 gC-CO2 m−2 yr−1 against +21.8 ± 3.4 gC-CH4 m−2 yr−1 in 2013) whereas in dry years it constituted a substantial carbon source (releasing up to +130 ± 70 gC-CO2 m−2 yr−1 and +2.6 ± 1.4 gC-CH4 m−2 yr−1 in 2015). Our findings demonstrate that the scenario of positive feedback between wetland carbon release and the present climate change trajectory is realistic and support the need of natural wetland preservation or rewetting. Our findings also indicate that conclusions drawn regarding a wetland's response to changing climate can depend strongly on the chosen period of analysis.

We investigated the variability of the aerosol scattering (σsp; 1974–2015) and absorption (σap; 2000–2015) coefficients at the Mauna Loa Observatory using surface in situ measurements. Although σsp decreased during the morning (1.85 ± 3.43 Mm–1 at 550 nm, 8–11 local standard time [LST]), it increased during the afternoon (3.72 ± 7.63 Mm–1 at 550 nm, 14–17 LST) due to the development of thermally induced boundary layer winds. No distinct diurnal variation was observed in σap. The obvious increase in σsp and σap during the spring under free troposphere conditions (8–11 LST) is attributed to long-range-transported aerosols from Asia, especially dust and pollution aerosols from Northeast Asia and biomass burning aerosols from Southeast Asia. Accordingly, σsp increased from 1974 till 2015 (at 1.89% year–1), whereas no significant trend was noted for either σsp or σap from 2000 till 2015. An increasing trend for σsp prevailed in air masses originating in Northeast Asia (+0.51 Mm–1 decade–1).

The atmospheric mixing state and emission rates play decisive roles in public exposure to urban air pollution. This study utilizes atmospheric radon measurements taken with the SM200 “stability monitor,” which reflect changes in the atmospheric mixing state, to evaluate and forecast air quality. Using six months (March–August 2016) of atmospheric radon measurements in Jinhua, China, we classify the nocturnal atmospheric stability conditions into four distinct categories, “well-mixed”, “weakly stable”, “moderately stable”, and “most stable”, by applying a modified radon-based stability technique. We calculate the atmospheric self-cleaning ability index (ASI) and evaluate it with the four-category stability scheme, and the results confirm that the atmospheric radon measurements reliably represent the atmospheric mixing state. Analyzing PM2.5, PM10, SO2, NO2, CO, and O3 measurements from three nearby stations during the campaign, we find that the pollutant concentrations and air quality index (AQI) values assigned using the aforementioned stability scheme are consistent with the defined atmospheric mixing states. We subsequently demonstrate that the modified radon-based stability method is suitable for targeting the most unfavorable air quality conditions and determining where the emissions originated. Finally, we propose a simple ASI-based model for predicting regional severe air pollution.

Ambient gamma dose, radon, and rainfall have been monitored in southern Bucharest, Romania, from 2010 to 2016. The seasonal cycle of background ambient gamma dose peaked between July and October (100–105 nSv h −1 ), with minimum values in February (75–80 nSv h −1 ), the time of maximum snow cover. Based on 10 m a.g.l. radon concentrations, the ambient gamma dose increased by around 1 nSv h −1 for every 5 Bq m −3 increase in radon. Radon variability attributable to diurnal changes in atmospheric mixing contributed less than 15 nSv h −1 to the overall variability in ambient gamma dose, a factor of 4 more than synoptic timescale changes in air mass fetch. By contrast, precipitation-related enhancements of the ambient gamma dose were 15–80 nSv h −1 . To facilitate routine analysis, and account in part for occasional equipment failure, an automated method for identifying precipitation spikes in the ambient gamma dose was developed. Lastly, a simple model for predicting rainfall-related enhancement of the ambient gamma dose is tested against rainfall observations from events of contrasting duration and intensity. Results are also compared with those from previously published models of simple and complex formulation. Generally, the model performed very well. When simulations underestimated observations the absolute difference was typically less than the natural variability in ambient gamma dose arising from atmospheric mixing influences. Consequently, combined use of the automated event detection method and the simple model of this study could enable the ambient gamma dose “attention limit” (which indicates a potential radiological emergency) to be reduced from 200 to 400% above background to 25–50%.

An economical and easy-to-implement technique is outlined by which the mean nocturnal atmospheric mixing state (“stability”) can be assessed over a broad (city-scale) heterogeneous region solely based on near-surface (2 m above ground level [a.g.l.]) observations of the passive tracer radon-222. The results presented here are mainly based on summer data of hourly meteorological and radon observations near Łodź, Central Poland, from 4 years (2008–2011). Behaviour of the near-surface wind speed and vertical temperature gradient (the primary controls of the nocturnal atmospheric mixing state), as well as the urban heat island intensity, are investigated within each of the four radon-based nocturnal stability categories derived for this study (least stable, weakly stable, moderately stable, and stable). On average, the most (least) stable nights were characterized by vertical temperature gradient of 1.1 (0.5)°C·m−1, wind speed of ~0.4 (~1.0) m·s−1, and urban heat island intensity of 4.5 (0.5)°C. For sites more than 20 km inland from the coast, where soils are not completely saturated or frozen, radon-based nocturnal stability classification can significantly enhance and simplify a range of environmental research applications (e.g. urban climate studies, urban pollution studies, regulatory dispersion modelling, and evaluating the performance of regional climate and pollution models).

A feasibility study is presented on a newly developed microdosimetry system named Octobox, for its application in low dose rate, mixed radiation environments. A full characterization of the device was performed at the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan, out-of-field of various heavy ion radiation fields — 290 MeV/u 12C, 230 MeV/u and 490 MeV/u 28Si and 400 MeV/u 20Ne ions, as well as a low dose rate 222Rn environment at the Australian Nuclear Sciences and Technology Organization (ANSTO). The device was shown to collect adequate statistics in a short period of time when compared to the MicroPlus probe with a single microdosimeter, while accurately measuring microdosimetric quantities and the corresponding average quality factor ( Q ¯ ) and dose equivalent (H) of the mixed radiation field. Good agreement of the microdosimetric spectra was also shown with Geant4 simulations for all presented ion fields. Based on the findings in this study, the Octobox is capable of being applied in mixed, low dose rate, radiation environments such as those encountered in space and aviation, as well as in underground mines for radiation protection purposes.

The SAFIRED (Savannah Fires in the Early Dry Season) campaign took place from 29 May until 30 June 2014 at the Australian Tropical Atmospheric Research Station (ATARS) in the Northern Territory, Australia. The purpose of this campaign was to investigate emissions from fires in the early dry season in northern Australia. Measurements were made of biomass burning aerosols, volatile organic compounds, polycyclic aromatic carbons, greenhouse gases, radon, speciated atmospheric mercury and trace metals. Aspects of the biomass burning aerosol emissions investigated included; emission factors of various species, physical and chemical aerosol properties, aerosol aging, micronutrient supply to the ocean, nucleation, and aerosol water uptake. Over the course of the month-long campaign, biomass burning signals were prevalent and emissions from several large single burning events were observed at ATARS.Biomass burning emissions dominated the gas and aerosol concentrations in this region. Dry season fires are extremely frequent and widespread across the northern region of Australia, which suggests that the measured aerosol and gaseous emissions at ATARS are likely representative of signals across the entire region of north Australia. Air mass forward trajectories show that these biomass burning emissions are carried north-west over the Timor Sea and could influence the atmosphere over Indonesia and the tropical atmosphere over the Indian Ocean. Here we present characteristics of the biomass burning observed at the sampling site and provide an overview of the more specific outcomes of the SAFIRED campaign.

Real-time monitoring of hourly concentrations of atmospheric Radon-222 (222Rn, radon) and some gaseous pollutants (SO2, CO, O3) was performed throughout 2013-2014 at Gosan station of Jeju Island, one of the cleanest regions in Korea, in order to characterize their background levels and temporal variation trend. The hourly mean concentrations of radon and three gaseous pollutants (SO2, CO, O3) over the study period were 2216±1100 mBq/m3, 0.6±0.7 ppb, 211.6±102.0 ppb, and 43.0±17.0 ppb, respectively. The seasonal order of radon concentrations was as fall (2644 mBq/m3)≈winter (2612 mBq/m3)>spring (2022 mBq/m3)>summer (1666 mBq/m3). The concentrations of SO2 and CO showed similar patterns with those of radon as high in winter and low in summer, whereas the O3 concentrations had a bit different trend. Based on cluster analyses of air mass back trajectories, the air mass frequencies originating from Chinese continent, North Pacific Ocean, and the Korean Peninsula routes were 30, 18, and 52%, respectively. When the air masses were moved from Chinese continent to Jeju Island, the concentrations of radon and gaseous pollutants (SO2, CO, O3) were relatively high: 2584 mBq/m3, 0.76 ppb, 225.8 ppb, and 46.4 ppb. On the other hand, when the air masses were moved from North Pacific Ocean, their concentrations were much low as 1282 mBq/m3, 0.24 ppb, 166.1 ppb, and 32.5 ppb, respectively.

Globally, modern mass transport systems whether by road, rail, water, or air generate airborne pollutants in both developing and developed nations. Air pollution is the primary human health concern originating from modern transportation, particularly in densely-populated urban areas. This review will specifically focus on the origin and the health impacts of carbonaceous traffic-related air pollutants (TRAP), including particulate matter (PM), volatile organic compounds (VOCs), and elemental carbon (EC). We conclude that the greatest current challenge regarding urban TRAP is understanding and evaluating the human health impacts well enough to set appropriate pollution control measures. Furthermore, we provide a detailed discussion regarding the effects of TRAP on local environments and pedestrian health in low and high traffic-density environments.

The concentrations of ozone (O3) and nitrogen oxides (NOx) were measured at two mountainous sites in Buk-Han (BH) and Gwan-Ak (GA) and at a reference site in Gwang-Jin (GJ), all in Seoul, South Korea, over a four-year period (2010–2013). The mean concentration (ppb) of NOx was comparable at the mountainous sites (22.9 ± 20.7 (BH) and 20.9 ± 16.9 (GA)) but about half the concentration at the reference site in GJ (47.8 ± 36.4). In contrast, the mean value (ppb) for O3 at the three sites exhibited a reversed pattern such as 40.2 ± 19.7 at GA, 28.6 ± 15.4 at BH, and 21.8 ± 18.3 at GJ. The concentration of NOx was higher in winter/fall relative to summer/spring at all three sites. Like the clear distinctions observed from the spatial distribution patterns, the seasonal trends conrasted sharply between NOx and O3. Results of a correlation analysis suggested that the distribution of O3 was significantly affected by meteorological parameters (e.g., TEMP, UV, and solar radiation). According to a back trajectory analysis, the highest O3 levels at both mountainous sites were caused by air masses passing over marine areas, while the effects of ozone precursors on ozone concentration were attributed to air masses originating from China and/or the mainland (S. Korea).

The stable isotopic composition of water vapour provides information about moisture sources and processes difficult to obtain with traditional measurement techniques. Recently, it has been proposed that the D-excess of water vapour (dv = δ2H − 8 × δ18O) can provide a diagnostic tracer of continental moisture recycling. However, D-excess exhibits a diurnal cycle that has been observed across a variety of ecosystems and may be influenced by a range of processes beyond regional-scale moisture recycling, including local evaporation (ET) fluxes. There is a lack of measurements of D-excess in evaporation (ET) fluxes, which has made it difficult to assess how ET fluxes modify the D-excess in water vapour (dv). With this in mind, we employed a chamber-based approach to directly measure D-excess in ET (dET) fluxes. We show that ET fluxes imposed a negative forcing on the ambient vapour and could not explain the higher daytime dv values. The low dET observed here was sourced from a soil water pool that had undergone an extended drying period, leading to low D-excess in the soil moisture pool. A strong correlation between daytime dv and locally measured relative humidity was consistent with an oceanic moisture source, suggesting that remote hydrological processes were the major contributor to daytime dv variability. During the early evening, ET fluxes into a shallow nocturnal inversion layer caused a lowering of dv values near the surface. In addition, transient mixing of vapour with a higher D-excess from above the nocturnal inversion modified these values, causing large variability during the night. These results indicate dET can generally be expected to show large spatial and temporal variability and to depend on the soil moisture state. For long periods between rain events, common in semi-arid environments, ET would be expected to impose negative forcing on the surface dv. Spatial and temporal variability of D-excess in ET fluxes therefore needs to be considered when using dv to study moisture recycling and during extended dry periods with weak moisture recycling may act as a tracer of the relative humidity at the oceanic moisture source.

We apply a simple objective measure of an airshed’s degree of ventilation and determine the impact on PM2.5 observations at Lucas Heights, Sydney, Australia. We extend the analysis of previous studies, which considered total PM2.5, by: using positive matrix factorisation to split the aerosol mass by source type; and using Radon-222 measurements as an independent indicator of ventilation and mixing. For this coastal airshed we found that for 64% of the time, conditions could be classified into four categories: local recirculation (LRC; 15%), stagnation (19.5%), regional recirculation (RRC; 10.9%), or ventilation (18.6%). Mean PM2.5 concentrations under recirculation (in this study separated into; LRC and RRC) were 33% higher than under stagnation and can be double that of concentrations under ventilation. Since the combination of LRC and RRC events account for around 26% of all events, recirculation effects on PM2.5 concentrations are significant. However, we found that airshed ventilation doesn’t affect PM2.5 concentrations from all sources evenly. Considering the three main sources of total PM2.5 at this site (vehicle exhaust 26.3%, secondary sulfate 23.7% and aged industrial sulfur 20.6%), conditions leading to the highest concentrations differ. The highest vehicle exhaust concentrations occur under LRC, the highest aged-industrial-sulphur concentrations occur under RRC, and secondary sulfur had similarly high concentrations under LRC and RRC. Under LRC the concentration from vehicle exhaust can be up to a factor of 3.9 greater than under ventilation. On a seasonal basis, RRC flow is most likely to occur in summer and spring (the warmer months of the year when sea breezes are more likely), whereas LRC conditions are more likely to occur in autumn and winter. These findings support those of previous studies, indicating that re-circulation can have a significant effect on PM2.5 concentrations in coastal airsheds, and the degree of impact can vary by source type.

Characterisation of the effects of varying atmospheric mixing states (stability) in urban climate studies has historically been hampered by problems associated with the complexity of the urban environment, representativity of measurement techniques, and the logistical and financial burdens of maintaining multiple long-term comprehensive measurement sites. These shortcomings, together with a lack of a consistent measurement approach, have limited our ability to understand the physical processes contributing to the urban heat island effect. In this study, we analyse 4 years of continuous hourly near-surface meteorological and atmospheric radon data from an urban–rural site pair in central Poland. A recently-developed radon-based stability classification technique, previously developed for urban pollution characterisation, is employed to characterise the Urban Heat Island Intensity (UHII) and other climatic factors over the full diurnal cycle by season and atmospheric mixing state. By characterising the UHII over a range of atmospheric mixing states in a statistically robust way, this technique provides an effective tool for assessing the efficacy of mitigation measures for urban climate effects in a consistent way over timescales of years to decades. The consistency of approach, ease of application, and unprecedented clarity of findings, provide a strong argument for atmospheric radon observations to be included as part of the ‘standard measurement suite’ for urban climate monitoring networks for non-coastal cities.

Cloud–radiation interactions over the Southern Ocean are not well constrained in climate models, in part due to uncertainties in the sources, concentrations, and cloud-forming potential of aerosol in this region. To date, most studies in this region have reported measurements from fixed terrestrial stations or a limited set of instrumentation and often present findings as broad seasonal or latitudinal trends. Here, we present an extensive set of aerosol and meteorological observations obtained during an austral summer cruise across the full width of the Southern Ocean south of Australia. Three episodes of continental-influenced air masses were identified, including an apparent transition between the Ferrel atmospheric cell and the polar cell at approximately 64∘ S, and accompanied by the highest median cloud condensation nuclei (CCN) concentrations, at 252 cm−3. During the other two episodes, synoptic-scale weather patterns diverted air masses across distances greater than 1000 km from the Australian and Antarctic coastlines, respectively, indicating that a large proportion of the Southern Ocean may be periodically influenced by continental air masses. In all three cases, a highly cloud-active accumulation mode dominated the size distribution, with up to 93 % of the total number concentration activating as CCN. Frequent cyclonic weather conditions were observed at high latitudes and the associated strong wind speeds led to predictions of high concentrations of sea spray aerosol. However, these modelled concentrations were not achieved due to increased aerosol scavenging rates from precipitation and convective transport into the free troposphere, which decoupled the air mass from the sea spray flux at the ocean surface. CCN concentrations were more strongly impacted by high concentrations of large-diameter Aitken mode aerosol in air masses which passed over regions of elevated marine biological productivity, potentially contributing up to 56 % of the cloud condensation nuclei concentration. Weather systems were vital for aerosol growth in biologically influenced air masses and in their absence ultrafine aerosol diameters were less than 30 nm. These results demonstrate that air mass meteorological history must be considered when modelling sea spray concentrations and highlight the potential importance of sub-grid-scale variability when modelling atmospheric conditions in the remote Southern Ocean.

Volatile organic compounds (VOCs) are important precursors to the formation of ozone and fine particulate matter, the two pollutants of most concern in Sydney, Australia. Despite this importance, there are very few published measurements of ambient VOC concentrations in Australia. In this paper, we present mole fractions of several important VOCs measured during the campaign known as MUMBA (Measurements of Urban, Marine and Biogenic Air) in the Australian city of Wollongong (34&deg, S). We particularly focus on measurements made during periods when clean marine air impacted the measurement site and on VOCs of biogenic origin. Typical unpolluted marine air mole fractions during austral summer 2012-2013 at latitude 34&deg, S were established for CO2 (391.0 &plusmn, 0.6 ppm), CH4 (1760.1 &plusmn, 0.4 ppb), N2O (325.04 &plusmn, 0.08 ppb), CO (52.4 &plusmn, 1.7 ppb), O3 (20.5 &plusmn, 1.1 ppb), acetaldehyde (190 &plusmn, 40 ppt), acetone (260 &plusmn, 30 ppt), dimethyl sulphide (50 &plusmn, 10 ppt), benzene (20 &plusmn, 10 ppt), toluene (30 &plusmn, 20 ppt), C8H10 aromatics (23 &plusmn, 6 ppt) and C9H12 aromatics (36 &plusmn, 7 ppt). The MUMBA site was frequently influenced by VOCs of biogenic origin from a nearby strip of forested parkland to the east due to the dominant north-easterly afternoon sea breeze. VOCs from the more distant densely forested escarpment to the west also impacted the site, especially during two days of extreme heat and strong westerly winds. The relative amounts of different biogenic VOCs observed for these two biomes differed, with much larger increases of isoprene than of monoterpenes or methanol during the hot westerly winds from the escarpment than with cooler winds from the east. However, whether this was due to different vegetation types or was solely the result of the extreme temperatures is not entirely clear. We conclude that the clean marine air and biogenic signatures measured during the MUMBA campaign provide useful information about the typical abundance of several key VOCs and can be used to constrain chemical transport model simulations of the atmosphere in this poorly sampled region of the world.

The Sydney Particle Study involved the comprehensive measurement of meteorology, particles and gases at a location in western Sydney during February/March 2011 and April/May 2012. The aim of this study was to increase scientific knowledge of the processes leading to particle formation and transformations in Sydney. In this paper we describe the methods used to collect and analyse particle and gaseous samples, as well as the methods employed for the continuous measurement of particle concentrations, particle microphysical properties and gaseous concentrations. This paper also provides a description of the data collected and is a meta data record for the data sets published in Keywood et al. (2016a) https://doi.org/10.4225/08/57903B83D6A5D and Keywood et al. (2016b) https://doi.org/10.4225/08/5791B5528BD63.

A recently-developed radon-based technique is used to investigate relative changes in summertime atmospheric stability at two sites in Slovenia with contrasting geographical settings. Although atmospheric stability for both sites (50 km apart) was shown to be governed by similar synoptic conditions, their contrasting settings caused differences in mixing conditions for each stability category. At the urban sub-Alpine site Ljubljana, situated within a topographic basin, wind speeds associated with the most stable conditions were 0.2–0.3 m s−1. By comparison, corresponding wind speeds for the near-coastal sub-Mediterranean site Ajdovscina, located at the foothills of the Trnovski gozd barrier, were 0–0.2 m s−1. The wind direction at Ljubljana under stable conditions (∼80°) was consistent with drainage flow into the basin along the Sava River valley. The corresponding wind direction at Ajdovscina was 20–40°, consistent with gentle katabatic drainage from the flanks of the Trnovski gozd barrier. After removing fetch effects on radon variability at each site, a large contrast in local contributions to the radon signal was noted: the diurnal amplitude of the local radon signal increased from ∼24 Bq m−3 at Ljubljana to ∼47 Bq m−3 at Ajdovscina. This difference was attributed to a greater nocturnal radon accumulation rate at Ajdovscina (3.5 Bq m−3 h−1 vs 2.1 Bq m−3 h−1) due to higher radon fluxes from flysch and carbonate rocks compared to the sea and lake sediments in the Ljubljana Basin. The ability of radon to consistently distinguish subtle changes in atmospheric mixing at sites with contrasting topographic settings indicates that it will be a powerful tool for characterising air quality in these complex environments. Specifically, diurnal radon cycles indicate that the capability of the atmosphere to dilute primary pollutants is considerably less in the basin environment.

We present findings from the Measurements of Urban, Marine and Biogenic Air (MUMBA) campaign, which took place in the coastal city of Wollongong in New South Wales, Australia. We focus on a few key air quality indicators, along with a comparison to regional scale chemical transport model predictions at a spatial resolution of 1 km by 1 km. We find that the CSIRO chemical transport model provides accurate simulations of ozone concentrations at most times, but underestimates the ozone enhancements that occur during extreme temperature events. The model also meets previously published performance standards for fine particulate matter less than 2.5 microns in diameter (PM2.5), and the larger aerosol fraction (PM10). We explore the observed composition of the atmosphere within this urban air-shed during the MUMBA campaign and discuss the different influences on air quality in the city. Our findings suggest that further improvements to our ability to simulate air quality in this coastal city can be made through more accurate anthropogenic and biogenic emissions inventories and better understanding of the impact of extreme temperatures on air quality. The challenges in modelling air quality within the urban air-shed of Wollongong, including difficulties in accurate simulation of the local meteorology, are likely to be replicated in many other coastal cities in the Southern Hemisphere.

A recently-developed radon-based technique is modified to quantify the seasonal influences of atmospheric stability on urban emissions in Lanzhou, China, based on 11 months of observations at three sites with contrasting pollution characteristics. Near-surface concentrations of primary (CO, SO 2 , NO x ) and secondary (O 3 ) gas phase pollutants responded to changing atmospheric stability in markedly different ways in winter and summer, primarily because monsoonal fetch changes strongly influenced the distance between measurement sites and their nearest upwind pollutant sources, but also due to mean diurnal changes in mixing depth. Typically, morning peak primary pollution concentrations increased by a factor of 2–5 from the most well-mixed to stable conditions, whereas nocturnal ozone concentrations reduced with increasing stability due to surface loss processes and the progressively reduced coupling between the nocturnal boundary layer and overlying free atmosphere. The majority of pollution exceedance events (cf. China National Air Quality Standard guideline values) occurred in winter, when all measurement stations were downwind of the city's main pollution sources, and were directly attributed to morning periods and stable atmospheric conditions. In the sheltered valley region of Lanzhou, extremes of winter nocturnal stability states represented a change in mean nocturnal wind speed of only 0.25 m s −1 (from 0.6 to 0.85 m s −1 ). Daily-integrated PM 10 concentrations increased by a factor of 2 in winter from the most well-mixed to stable conditions, and were usually above guideline values at the industrial and residential sites for all atmospheric stability conditions. In summer, however, daily mean PM 10 exceedances usually only occurred at the industrial site, under stable conditions. Finally, a simple model – based on mean radon concentrations between 1900 and 0400 h – is proposed to predict haze conditions in the city prior to commencement of the peak morning commuting time.

Ion Beam Analysis (IBA) techniques were used to assign nine years of PM2.5 observations to seven source types, at Lucas Heights, a topographically complex urban fringe site of Sydney. The highest contributions to total PM2.5 were from motor vehicles (Autos, 26.3%), secondary sulfur (2ndryS, 23.7%), a mixture of industry and aged sea air (IndSaged, 20.6%), and smoke (Smoke, 13.7%). The Autos contribution was highest in winter, whereas 2ndryS was highest in summer, indicating that mitigation measures targeting SO2 release in summer and vehicle exhaust in winter would be most effective in reducing the PM2.5 concentrations at this site. Since concentrations of particulate matter can be significantly affected by local meteorology, generalised additive model (GAM) techniques were employed to investigate relationships between PM2.5 source types and meteorological conditions. The GAM predictors used included: time (seasonal to inter-annual variations), mixing layer depth, temperature, relative humidity, wind speed, wind direction, and atmospheric pressure. Meteorological influences on PM2.5 variability were found to be 58% for soil dust, 46% for Autos, 41% for total PM2.5, and 35% for 2ndryS. Effects were much smaller for other source types. Temperature was found to be an important variable for the determination of total PM2.5, 2ndryS, IndSaged, Soil and Smoke, indicating that future changes in temperature are likely to have an associated change in aerosol concentrations. However, the impact on different source types varied. Temperature had the highest impact on 2ndryS (sometimes more than a factor of 4 increase for temperatures above 25 °C compared to temperatures under 10 °C) and IndSaged, being predominantly secondary aerosols formed in the atmosphere from precursors, whereas wind speed and wind direction were more important for the determination of vehicle exhaust and fresh sea salt concentrations. The marginal effect of relative humidity on 2ndryS increased up to relative humidity of 70–80% and then plateaued, confirming previous findings that (NH4)2SO4 is present in the solid phase below relative humidity of about 80%.