The relationship between airborne small ions and particles in urban environments

Observations of atmospheric air ions at most geographic areas have been undertaken, but there are still very few observations at middle-latitude semi-arid areas throughout the world. To quantify characteristics of small air ions in semiarid areas of China, measurements of small air ions and particulate matter (PM 10 ) were conducted at 16 different sites in Xi'an (34°26′N, 108°94'E), China, from August 2009 to July 2010 along with meteorological parameters. The influences of meteorological parameters and PM 10 concentration on small air ions as well as their influence mechanisms were discussed in detail. The results showed that both spatial and temporal distributions of small ions were uneven in Xi'an city. Spatially, the concentration of small ions increased gradually from city center to the suburbs. The mean annual concentration of small negative ions was in the range of 200-400 cm -3 with the mean value of 261 ± 39 cm -3 at urban areas, while more than 500 cm -3 at suburban areas. Significant seasonal variations of small ions were observed with highest level in summer, followed by spring and autumn, and lowest in winter at various types of sites. The positive correlations were found between small ions concentration and temperature as well as relative humidity, while negative correlation between the small ions concentration and PM 10 concentration. Air ions concentration was also applied to the assessment of air quality in Xi'an. The assessment results indicated that the air quality was better at suburban areas than at urban areas, suggesting that the unipolarity model is reasonable to indicate air cleanness.

Section: Relationship Between Small Air Ions and Pm 10supporting

confidence: 81%

Section: Introductionmentioning

confidence: 94%

Section: Seasonal Variations In Concentrations Of Small Air Ionsmentioning

confidence: 99%

See 1 more Smart Citation

Characteristics of Atmospheric Small Ions and Their Application to Assessment of Air Quality in a Typical Semi-Arid City of Northwest China

Guo

Wang

et al. 2015

“…The magnitudes and COU of the small ion concentrations are consistent with that found by Ling et al (2013) at close proximity to the present monitoring location using two Alphalab air ion counters. They found COU's for small ions of 1.40 at a site very similar to the present site, about 2 km away, and 1.30 at an urban residential site located about 9 km to the north of the present site.…”

Section: Relationship Between Positive and Negative Ion Concentrationssupporting

confidence: 75%

Charging State of Aerosols during Particle Formation Events in an Urban Environment and Its Implications for Ion-Induced Nucleation

Jayaratne

Ling

Morawska

2016

Self Cite

The aim of this study was to investigate the charging state of atmospheric ions during particle formation (PF) events in an urban environment. We measured small ion (charged cluster) and large ion (charged particle) concentrations over a period of 13 months in Brisbane, Australia, using a neutral cluster and air ion spectrometer (NAIS) and obtained 245 complete days of data. PF events were observed on 110 days which count as 45% of the total. On the average, the positive small ion concentration was 40% higher than the negative. The positive large ion concentration was 20% higher than the negative. Generally, small ion concentrations peaked during the night, while large ion concentrations were a maximum during the day. Next, we classified the results into days on which there was a PF event and when there was not. We showed that PF events have a profound effect on small and large ion concentrations in the environment; the small ion concentrations decreased by about 30% while large ion concentrations increased by up to 100%. We identified two phenomena that have a bearing on ion-induced nucleation. Firstly, the fraction of particles that were charged consistently decreased during PF events and rarely exceeded the equilibrium value, suggesting that the formation process was not significantly influenced by an ion-induced mechanism. Secondly, small ion concentrations were higher in the pre-dawn hours of PF event days than on other days, while the fraction of clusters that were charged often showed an increase immediately prior to a PF event, both observations supporting an ion-induced mechanism of PF. This study serves as basis for future work explaining these observations.

“…Our main aim was to investigate the effect of PNC on the ambient CIC. Although there are many studies of the effect of PNC on CIC (Retalis et al, 2009;Hirsikko et al, 2011;Ling et al, 2013), there are few reports, if any, of the interaction rate of cluster ions and particles during rapid PNC variations that tend to occur frequently in the environment.…”

Section: Introductionmentioning

confidence: 99%

Suppression of Cluster Ions during Rapidly Increasing Particle Number Concentration Events in the Environment

Jayaratne

Ling

Morawska

2015

Self Cite

We show that the cluster ion concentration (CIC) in the atmosphere is significantly suppressed during events that involve rapid increases in particle number concentration (PNC). Using a neutral cluster and air ion spectrometer, we investigated changes in CIC during three types of particle enhancement processes -new particle formation, a bushfire episode and an intense pyrotechnic display. In all three cases, the total CIC decreased with increasing PNC, with the rate of decrease being greater for negative CIC than positive. We attribute this to the greater mobility, and hence the higher attachment coefficient, of negative ions over positive ions in the air. During the pyrotechnic display, the rapid increase in PNC was sufficient to reduce the CIC of both polarities to zero. At the height of the display, the negative CIC stayed at zero for a full 10 min. Although the PNCs were not significantly different, the CIC during new particle formation did not decrease as much as during the bushfire episode and the pyrotechnic display. We suggest that the rate of increase of PNC, together with particle size, also play important roles in suppressing CIC in the atmosphere.