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Research into the adverse health effects of air pollution exposure has repeatedly considered smaller particles, to the point where particle number concentration might be a more relevant metric than mass concentration. Here, we highlight some historical research which developed metrics for air pollution severity based on particle number concentration. Because this work was published in a national journal and prior to the internet and open access, this historical research is not easy to find, and it was more through the history of the aerosol research community in Ireland that this work is now being presented. Multiple online searches for published research papers on "particle number concentrations" and "air pollution severity" were undertaken. Even when specific searches were undertaken using the author names and publication year, these featured papers were not found on any internet search. O'Dea and O'Connor proposed that air pollution severity could be classified based on particle number concentration of condensation nuclei, with 'little' air pollution <50 × 103 particles per cm3, 'mean' 50–70 × 103 particles per cm3, 'strong' 70–100 × 103 particles per cm3, and 'very strong' >100 × 103 particles per cm3. Applying their assumptions on density and mean particle size, equated to mass concentrations for a mean of 6 µgm−3, strong at 8.5 µgm−3, and very strong >10 µgm−3. These are consistent with the current WHO guideline values for PM2.5. Additionally, we highlight the 1955 work by Burke and Nolan on the retention of inhaled particles, where ~40% of the inhaled number concentration is retained in the respiratory system. This is also consistent with the more recently published work on particle retention. In summary, the proposed categories of pollution severity, based on number concentrations, could form a basis for the development of future guidelines. This paper highlights that sometimes research has already been published, but it is difficult to find. We challenge researchers to find publications from their own countries which pre-date the WWW to inform current and future research. Additionally, there is scope for a repository for such information on historical publications. We have presented historical research on aerosol number concentrations, classifications of air pollution severity, and particle retention, which present lessons for current researchers. [ABSTRACT FROM AUTHOR]

Accurate air temperatures underpin environmental research. Most professional meteorological air temperature measurements still expose thermometers within traditional, naturally ventilated screens. Their representation of true air temperature depends on screen airflow, and therefore local winds. Accuracies of daily maximum (Tmax) and minimum (Tmin) air temperatures are assessed by comparison between a naturally ventilated large conventional screen and a co‐located aspirated reference screen. In over 1200 days' data, the naturally ventilated Tmin and Tmax both showed small (median < 0.06°C) cold bias, but, in 1% of cases, warm Tmax bias and cold Tmin bias >|1°C|. The Tmin cold bias is associated with calm clear nights, and the Tmax warm bias events with calm winter days at low sun angles, allowing solar heating of the screen. The prevalence of poor natural ventilation, potentially affecting Tmin and Tmax, is estimated across European sites. Poor ventilation occurred at Tmin for 12% of values, and at Tmax for 4%. Climatological averaging will reduce these effects, but, without corroborating wind data, statistical changes in Tmin or Tmax, including identifying "Tropical Nights" (Tmin > 20°C) or occurrences of winter extremes, may have limited value. Wider adoption of aspirated thermometer screens, with an initial overlap period, will largely eliminate these effects. [ABSTRACT FROM AUTHOR]

Releasing charge into natural droplet systems such as fog and clouds offers a route to influence their properties. To facilitate charge release across a wide range of altitudes and meteorological circumstances—such as developing clouds—a charge emitter has been developed for integration with the conventional cloud-seeding flares carried by crewed cloud-seeding aircraft. This allows charge emitters to be used alongside, or instead of, conventional particle releasing flares. The charge emitter flare system is self-contained and self-powered, and includes internal monitoring and recording of its operating parameters. Using this "flare emitter" approach, successful charge emission has been demonstrated in level flight, at 3 km altitude, likely to have exceeded natural ion concentrations by several orders of magnitude. This quantitative verification of successful charge emission can underpin further physically based experiments on the effectiveness of charge release in cloud seeding. [ABSTRACT FROM AUTHOR]

Atmospheric electricity measurements, principally of the hourly potential gradient (PG), were made continuously at Eskdalemuir Observatory, Scotland (55.314° N, 3.206° W), between 1911 and 1981. Air ion properties were also determined. The sensing apparatus for PG measurement at Eskdalemuir initially used a Kelvin water dropper potential equaliser (1911–1936), followed by a radioactive probe from 1936 and, from 1965, a horizontal stretched wire sensor at 0.5 m, all attached to recording devices. Monthly mean PG data from these instruments are now available digitally. Originally, the data were classified into undisturbed and disturbed days, using the chart record (electrogram). This approach has deficiencies at Eskdalemuir due to mist, fog and calm conditions, which can influence the mean PG despite the day appearing undisturbed on the electrogram. Nevertheless, a correlation with Pacific Ocean temperature fluctuations is apparent in the Eskdalemuir PG data between 1911 and 1950. As at Lerwick, there was an abrupt decrease in the PG caused by nuclear weapon detonations in the late 1950s and early 1960s. The 1950s PG decrease began at Eskdalemuir before that at Lerwick, for which possible additional local factors are evaluated. [ABSTRACT FROM AUTHOR]

Measurement of the emission current at a high voltage is necessary in monitoring ion production from a corona source, to provide independent confirmation of operation. The wide common mode range required is usually obtained through an isolated system, which requires isolated power to operate, adding complexity and volume. Passing the current through a light-emitting diode (LED) provides an alternative measurement method as the LED's brightness can be used to signal the current's magnitude. The forward voltage loss across the LED is negligible compared with the emitter voltage. Selection of a discrete LED for this task rather than using one within a standard integrated optocoupler package improves the low current sensitivity by two orders of magnitude. A high efficiency discrete infrared LED–photodiode pair is demonstrated to provide measurements of corona currents between 0.2 and 20 µA using a second LED–photodiode pair for analog linearity compensation. The inherent simplicity is well suited to new applications of ion emission in propulsion and weather modification. [ABSTRACT FROM AUTHOR]

The beginning, peak and end of the eclipse are marked as in Figure 4. gl Surface air temperature averaged from 254 MMS sites shows a marked reduction in the rate of increase of temperature around the time of peak eclipse (Figure 6a). In addition, the maximum and minimum temperatures recorded every 10min were also available for many of these sites, so we were alternatively able to quantify the temperature decrease based on the highest temperature between 0830 and 0930 utc (near the start of the eclipse) and the lowest temperature between 1000 and 1100 utc (around the eclipse peak). Iceland Conditions here too were generally cloudy during the eclipse (Table S3), but the eclipse magnitude was much larger than over the British Isles, being typically ~70% magnitude or ~60% coverage of the solar disk at peak eclipse (Figure 1). Also, all of the nine sites with relatively less cloud cover had significant changes in cloud cover during the eclipse, so were not a suitable subset to use for studying the eclipse influence on surface air temperature. [Extracted from the article]

The 11th CTR Wilson Meeting on atmospheric electricity took place at the University of Bath in November 2023. The meeting brought together UK and international researchers to discuss various topics related to atmospheric electricity, including lightning, atmospheric ionization, and the global electric circuit. Presentations covered subjects such as lightning location, the impact of aerosol pollution on lightning activity, and the use of radio telescope data to study lightning events. Other topics included the relationship between climate change and lightning incidence, the correlation between thunder days and cloud-to-ground strikes, and the effect of climate change on lightning intensity. The meeting also featured discussions on historical potential gradient records, point-discharge sensors, and the behavior of potential gradient in fog. The event concluded with a presentation on modeling the electric and magnetic fields produced by dust devils on Mars and a discussion of a recently published book on lightning research in Arizona. The meeting included a poster session where researchers presented their work on topics such as lightning climatology, fair weather potential gradient classification methods, aircraft charge emitter systems, and volcanic ash charging. [Extracted from the article]

During 4 decades, from 1950 to 1990, atmospheric electricity measurements as well as other environmental measurements were made by Reinhold Reiter at several sites close to Garmisch-Partenkirchen. The quantities determined included the atmospheric potential gradient, the vertical current, and the ion concentrations. Observations made at the Mount Wank site (47 ∘ 30 ′ N, 11 ∘ 09 ′ E; 1780 m) from 1 August 1972 to 31 December 1983 are available in digital form. [ABSTRACT FROM AUTHOR]